JP2016015491A - Easy adhesive polyester film for solar cell and front sheet using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an easy adhesive polyester film for a solar cell which is excellent in adhesiveness and transparency, and a front sheet using the same.SOLUTION: The easy adhesive polyester film for a solar cell has a coating layer on at least one surface thereof. The coating layer is mainly composed of a urethane resin and a blocked isocyanate. The mass ratio (urethane resin/blocked isocyanate) of the urethane resin to the blocked isocyanate in the coating layer is 1/9-8/2. The dissociation temperature of the blocked isocyanate is 130°C or lower, and the boiling point of a blocking agent is 180°C or higher.

Description

  The present invention relates to an easily adhesive polyester film for solar cells and a front sheet sheet using the same. Specifically, the present invention relates to a polyester film that is excellent in adhesion with a sealant even under high temperature and high humidity and has high transparency when used on a surface that contacts a sealant of a solar cell, and a front sheet using the same. .

  In recent years, solar cells have attracted attention as an energy means to replace petroleum energy that causes global warming, and the demand for solar cells has increased. A solar cell is a solar power generation system that directly converts solar energy into electricity. As a solar cell element, semiconductors such as single crystal silicon, polycrystalline silicon, and amorphous silicon, compound-based materials, and organic dyes are used. Yes. In order to protect such elements over a long period of time (approximately 20 years or more), such a solar cell element is generally wired in series or in parallel with several to several tens of solar cell elements. Done and unitized. A unit incorporated in this package is called a solar cell module.

  Here, a solar cell module generally covers a surface to which sunlight is applied with glass, fills a gap with a sealing material for a solar electronic element, and has a plurality of layers such as a heat-resistant and weather-resistant plastic material called a back sheet on the back surface. It is the structure protected by the protective sheet which consists of a structure. As a sealing material filling the solar cell element, an olefin resin such as ethylene / vinyl acetate copolymer resin (hereinafter EVA) or polyvinyl butyral resin (hereinafter PVB) is used. Using these sealing materials, a module is produced 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, interest in plastic films such as polyester having flexibility in terms of impact resistance and weight reduction has increased (Patent Documents 1 to 3). 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 4 to 7).

JP 2010-186932 A JP 2007-253463 A JP 2006-261287 A JP 2006-152013 A JP 2006-320991 A JP 2007-48944 A JP 2007-136911 A

  In order to improve the photoelectric conversion efficiency of the solar cell element, high transparency is required for the front sheet used for the front surface of the solar cell. Solar cell modules that are used outdoors under severe environmental conditions are expected to have a lifespan of 20 years or longer. Therefore, it was considered that not only the initial adhesiveness but also the adhesive easily adhesive film used as a member needs to maintain the adhesive property for a long period of time under high temperature and high humidity. However, when an easy-adhesion layer containing a crosslinking agent is provided in order to improve the adhesion with the sealant, the transparency may be lowered.

  In addition, from the viewpoint of improving productivity and preventing deterioration, various composition types including additives such as a crosslinking agent and an ultraviolet absorber are used for the sealing material. It has been adopted. For example, in the case of a sealing material of the standard cure type, heat treatment (for example, 30 to 50 minutes at 140 to 160 ° C.) is performed after temporary bonding by thermocompression bonding (for example, 90 to 130 ° C. for 5 to 10 minutes), and sealing is performed slowly. Adhesive conditions for curing the stop material are employed. On the other hand, in a fast-curing type sealing material, an adhesive condition is adopted in which thermocompression bonding (for example, 15 to 20 minutes at 140 to 160 ° C.) is performed in a short time and the sealing material is rapidly cured. 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.

  In view of the above problems, the present invention provides an easy-adhesive polyester film for solar cells that is excellent in adhesiveness with a sealant and has high transparency. More preferably, the present invention provides an easy-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.

  As a result of intensive studies to solve the above problems, the inventor surprisingly has a urethane resin and a blocked isocyanate as main components, the dissociation temperature of the blocked isocyanate is 130 ° C. or less, and the boiling point of the blocking agent is The present inventors have found that by using a coating layer having a temperature of 180 ° C. or higher, excellent adhesiveness with a sealant and high transparency are achieved, and the present invention has been achieved.

The above-described problem can be achieved by the following solution means.
(1) A polyester film having a coating layer on at least one surface, wherein the coating layer is mainly composed of a urethane resin and a blocked isocyanate, and a mass ratio of the urethane resin and the blocked isocyanate in the coating layer (urethane resin / block isocyanate). ) Is 1/9 to 8/2, 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.
(2) The said easily adhesive polyester film for solar cells whose said urethane resin is a urethane resin which uses aliphatic polycarbonate polyol as a structural component.
(3) In the infrared spectrum of the coating layer, the absorbance at the peak near 1460 cm ⁻¹ derived from the aliphatic polycarbonate component (A ₁₄₆₀ ) and the absorbance at the peak near 1530 cm ⁻¹ derived from the urethane component (A ₁₅₃₀ ) ratio _(a 1460 _/ a ₁₅₃₀₎ is 0.50 to 1.55, the sun highly adhesive polyester film for batteries.
( 4 ) The solar cell front sheet | seat which laminated | stacked the said easily adhesive polyester film for solar cells.

  The easily adhesive polyester film for solar cells of the present invention is excellent in adhesiveness with a sealant and has 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, as a preferred embodiment of the present invention, 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 adhesion with a sealing material is good. is there.

(Polyester film)
The polyester resin constituting the substrate in the present invention includes polyethylene terephthalate, polybutylene terephthalate, polyethylene-2,6-naphthalate, polymethylene terephthalate, and copolymerization components such as diethylene glycol, neopentyl glycol, and polyalkylene glycol. A diol component, a polyester resin copolymerized with a dicarboxylic acid component such as adipic acid, sebacic acid, phthalic acid, isophthalic acid, or 2,6-naphthalenedicarboxylic acid can be used.

  The polyester resin suitably used in the present invention mainly contains at least one of polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate as a constituent component. Among these polyester resins, polyethylene terephthalate is most preferable from the balance between physical properties and cost. Moreover, these polyester films can improve chemical resistance, heat resistance, mechanical strength, etc. by biaxially stretching.

  Although it does not specifically limit as polycondensation used for manufacture of polyester, Ammonium trioxide is suitable since it is an inexpensive catalyst with the outstanding catalyst activity. It is also preferable to use a germanium compound or a titanium compound. More preferable polycondensation catalysts include a catalyst containing aluminum and / or its compound and a phenol compound, a catalyst containing aluminum and / or its compound and a phosphorus compound, and a catalyst containing an aluminum salt of a phosphorus compound.

  In order to obtain a high durability as a member for solar cell, the intrinsic viscosity of the polyester film is preferably 0.60 to 0.90 dl / g, more preferably 0.62 to 0.85 dl / g, Preferably it is 0.65-0.8 dl / g. When the intrinsic viscosity value is lower than 0.60 dl / g, the durability is not sufficient, and when it is higher than 0.90 dl / g, the back pressure in the melting process is increased, and thus the productivity is lowered. Further, it is not preferable because thermal deterioration is accelerated by shearing heat generation. In order to obtain high hydrolysis resistance, the polyester film of the present invention preferably has a carboxyl terminal concentration of 25 eq / ton or less with respect to the polyester.

  The polyester film of the present invention may be a single-layer polyester film or a polyester film having at least three layers having an outermost layer and a center layer.

  In this invention, when high transparency is calculated | required as a front sheet | seat, the structure which does not contain particle | grains substantially in a base film, but makes a coating layer contain particle | grains only is preferable. Further, in order to achieve both transparency and workability, the base film has a three-layer laminated structure, the outermost layer (A layer in the case of the above-mentioned two types and three layers) contains particles, and the central layer (the above two types) In the case of three layers, the B layer) may be substantially free of particles.

  Note that “substantially free of inert particles” means, for example, in the case of inorganic particles, when the element derived from the particles is quantitatively analyzed by fluorescent X-ray analysis, it is less than 50 ppm, preferably less than 10 ppm. Preferably, the content is below the detection limit. This is because even if particles are not added positively, contaminants derived from foreign substances and raw material resin or dirt attached to the line or equipment in the film manufacturing process may be peeled off and mixed into the film. It is.

  The type and content of the particles contained in the outermost layer may be inorganic particles or organic particles, and are not particularly limited, but include metal oxidation such as silica, titanium dioxide, talc, and kaolinite. Examples thereof include inorganic particles that are inert to polyesters such as products, calcium carbonate, calcium phosphate, and barium sulfate. Any one of these inert inorganic particles may be used alone, or two or more thereof may be used in combination.

  The particles preferably have an average particle size of 0.1 to 3.5 μm. The lower limit of the average particle diameter is more preferably 0.5 μm, further preferably 0.8 μm, and still more preferably 1.0 μm. Further, the upper limit of the average particle is more preferably 3.0 μm, still more preferably 2.8 μm. If the average particle size is less than 0.1 μm, sufficient handling properties cannot be obtained. When it exceeds 3.5 μm, coarse protrusions are likely to be generated.

  These particles are preferably porous particles, particularly porous silica. The porous particles are preferable because they are easily deformed into a flat shape when stretched in the film forming process and the decrease in transparency is small.

  The content of inorganic particles in the outermost layer is preferably 0.01 to 0.20 mass% with respect to the polyester constituting the outermost layer. The lower limit of the concentration is more preferably 0.02% by mass, and further preferably 0.03% by mass. Further, the upper limit of the concentration is more preferably 0.15% by mass, and further preferably 0.10% by mass. If it is less than 0.01% by mass, sufficient handling properties cannot be obtained. If it exceeds 0.2% by mass, the transparency is lowered, which is not preferable.

The average particle diameter of the particles can be measured by the following method.
The particles are photographed with an electron microscope or an optical microscope, and the maximum diameter of 300-500 particles (in the case of porous silica, the aggregate size) is such that the size of one smallest particle is 2-5 mm. Particle diameter) is measured, and the average value is taken as the average particle diameter. Moreover, when calculating | requiring the average particle diameter of the particle | grains in the coating layer of a laminated film, the cross section of a laminated film is image | photographed by 120,000 times magnification using a transmission electron microscope (TEM), and the largest diameter of a particle | grain is calculated | required. Can do.

  A known method can be adopted as a method of blending the above-mentioned particles with polyester. For example, it can be added at any stage for producing the polyester, but it is preferably added as a slurry dispersed in ethylene glycol or the like at the stage of esterification or after the end of the ester exchange reaction and before the start of the polycondensation reaction. The polycondensation reaction may proceed. Also, a method of blending a slurry of particles dispersed in ethylene glycol or water with a vented kneading extruder and a polyester raw material, or a method of blending dried particles and a polyester raw material using a kneading extruder It can be carried out.

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

  A known substance is used for the ultraviolet absorber used in the present invention. 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 the organic ultraviolet absorber include benzotoazole, benzophenone, cyclic imino ester, 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, benzotoazole 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 mix it. Is preferably low. As a condition for producing the master batch, it is preferable to use a kneading extruder and to extrude it 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 an antioxidant, a light resistance agent, an antigelling agent, an organic wetting agent, an antistatic agent, and a surfactant.

  Although the thickness of the polyester film used as the base material of this invention is not specifically limited, 20-500 micrometers is preferable, More preferably, it is 25-450 micrometers, More preferably, it is 30-300 micrometers. When the substrate thickness is thin, the influence of heat shrinkage is large, and the adhesiveness after high temperature and high humidity treatment may be reduced. If it is thick, it cannot be wound as a roll.

  When used as a front sheet, it is desirable that the highly adhesive polyester film for solar cell of the present invention has high transparency in terms of photoelectric conversion efficiency. The transparency of the film is preferably less than 5.0%, more preferably less than 4.5%, and still more preferably 4.3% or less.

(Coating layer)
It is important that the easily adhesive polyester film for solar cells of the present invention has a coating layer 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. It is. 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 layer.

  A flexible urethane resin is preferably used in order to impart easy adhesion, but it is considered desirable to actively introduce a cross-linked structure to make a hard coating layer from the viewpoint of improving the adhesion of the coating layer. It was. 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 apply stably 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 block 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 was thought to be because minute uneven pinholes were formed on the coated surface when the dissociated blocking agent volatilized at a high temperature.

  Therefore, as a result of intensive studies, the inventor is excellent in adopting a coating layer 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. It has been found that high adhesion 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.

  According to the aspect described above, the present invention can exhibit strong adhesiveness with a sealing material and can improve adhesiveness (moisture heat resistance) under high temperature and high humidity. Further, the configuration of the present invention will be described in detail below.

(Urethane resin)
The urethane resin of the present invention includes at least a polyol component and a polyisocyanate component as constituent components, and further includes a chain extender as necessary. The urethane resin of the present invention is a polymer compound in which these constituent components are mainly copolymerized 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 the like acrylic polyols. 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 urethane resin of this invention. From the viewpoint of preventing yellowing by sunlight of the present invention, it is preferable to use an aliphatic polycarbonate polyol. The components 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 sealant, the vicinity of 1460 cm ⁻¹ derived from the aliphatic polycarbonate component measured by infrared spectroscopy of the coating layer. The ratio (A ₁₄₆₀ / A ₁₅₃₀ ) of 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, it was considered desirable to make the coating layer rigid and strong in forming the coating layer from the viewpoint of improving the durability of the coating layer. However, in the present invention, the polyurethane resin comprising an aliphatic polycarbonate polyol as a constituent component controls the absorbance by infrared spectroscopy within a certain range, thereby exhibiting strong adhesion and adhesion under high temperature and high humidity heat. 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 the module is packaged, thermocompression bonding is performed at a high temperature in a configuration in which a glass film / a sealing material / a polyester film having a coating layer (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 kinds of sealing materials and bonding conditions. In particular, in the standard cure type that takes a high temperature for a long time, the stress change accompanying the thermal contraction becomes large. As a result, it was considered that the stress could not be alleviated and the adhesiveness with the sealing material was 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 was considered that the above stress could not be endured, the sealing material was peeled off, and the adhesiveness under high temperature and high humidity was 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 ) and the urethane component in the vicinity of 1460 cm ⁻¹ derived from the aliphatic polycarbonate component measured by infrared spectroscopy. When the ratio (A ₁₄₆₀ / A ₁₅₃₀ ) of the absorbance (A ₁₅₃₀ ) in the vicinity of 1530 cm ⁻¹ of the origin is 0.50 to 1.55, the above characteristics can be more suitably achieved. 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. This makes it possible to relieve stress due to thermal shrinkage of the film during thermal bonding at high temperatures, so that strong adhesiveness can be obtained even under various sealing materials and bonding conditions. We believe that the coating layer can be prevented from deteriorating because it retains heat resistance and hydrolysis resistance even in wet environments.

Here, the absorbance in the vicinity of 1460 cm ⁻¹ (A ₁₄₆₀ ) is derived from the bending vibration specific to the C—H bond in 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, but the lower limit of the ratio (A ₁₄₆₀ / A ₁₅₃₀ ) is preferably 0.60, more preferably. Is 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, so that the coating strength and moisture and heat resistance are reduced. May decrease.

Examples of the aliphatic polycarbonate polyol include aliphatic polycarbonate diols and aliphatic polycarbonate triols, and aliphatic polycarbonate diols can be preferably used. Examples of the aliphatic polycarbonate diol that is a constituent of the urethane resin of the present invention 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- Aliphatic polycarbonate diols obtained by reacting one or more diols such as cyclohexanedimethanol with carbonates such as dimethyl carbonate, diphenyl carbonate, ethylene carbonate, and phosgene. It is below. The number average molecular weight of the aliphatic polycarbonate diol is preferably 1500 to 4000, and 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. If the number average molecular weight of the aliphatic polycarbonate diol is large, the absorbance (A ₁₄₆₀ ) near 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 of the present invention include aromatic aliphatic diisocyanates such as xylylene diisocyanate, isophorone diisocyanate and 4,4-dicyclohexylmethane diisocyanate, and 1,3-bis (isocyanatomethyl) cyclohexane. Such as alicyclic diisocyanates such as hexamethylene diisocyanate and aliphatic diisocyanates such as 2,2,4-trimethylhexamethylene diisocyanate; Isocyanates. 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.

Chain extenders 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, and 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. Moreover, the point which provides the softness | flexibility of an application layer has preferable the chain extender of the diol and the diamine whose length of carbon number of a main chain is 4-10. 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, linear 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. The “water-soluble” means that it dissolves in water or an aqueous solution containing less than 50% by mass of a water-soluble organic solvent.

  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 introduced.

  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, tri-n-butylamine, N such as N-methylmorpholine and N-ethylmorpholine. -N-dialkylalkanolamines such as alkylmorpholines, N-dimethylethanolamine, N-diethylethanolamine and the like. These can be used alone or in combination of two or more.

  In order to impart water solubility, when a polyol compound having a carboxylic acid (salt) group is used as a copolymerization component, the composition molar ratio of the polyol compound having a carboxylic acid (salt) group in the urethane resin is the same as that of the urethane resin. When the total polyisocyanate 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 adhesiveness by partial mixing, From the viewpoint of stress relaxation of the coating layer, it is preferable because it is easy to achieve suitable flexibility.

  In the urethane resin of the present invention, a crosslinking group may be introduced into the resin itself in order to improve adhesion after high temperature and high humidity. 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 of the present invention may be contained in order to improve adhesiveness. For example, a urethane resin, an acrylic resin, a polyester resin, or the like containing polyether or polyester as a constituent component can 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 layer. The blocked isocyanate can be obtained by reacting a polyisocyanate with a block agent. The dissociation temperature and boiling point can be measured by differential thermal analysis.

  The dissociation temperature of the blocked isocyanate is preferably 130 ° C or lower, more preferably 125 ° C or lower, and still more 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. Although the upper limit of dissociation temperature will not be specifically limited if it is room temperature or more for stabilization of a coating liquid, 50 degreeC or more is preferable, 60 degreeC or more is more preferable, 80 degreeC or more is further more preferable.

  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 preferably 180 ° C or higher, more preferably 190 ° C or higher, further preferably 200 ° C or higher, and further preferably 210 ° C or higher. The higher the boiling point of the blocking agent, the more the volatilization of the blocking agent is suppressed by the heat application in the film-forming process in the drying process or in-line coating method after application of the coating solution, and the occurrence of minute unevenness on the coated surface is suppressed. , Transparency of the film is improved. The upper limit of the boiling point of the blocking agent is not particularly limited, but it seems that the upper limit is about 300 ° C. from the viewpoint of productivity. Since the boiling point is related to the molecular weight, in order to increase the boiling point of the blocking agent, it is preferable to use a blocking agent having a large molecular weight. The molecular weight of the blocking agent is preferably 50 or more, more preferably 60 or more, and more preferably 80 or more. preferable.

The dissociation temperature used for the blocked isocyanate of the present invention is 130 ° C. or lower, and the blocking agent has a boiling point of 180 ° C. or higher.
Bisulfite compounds: Sodium bisulfite, etc.
Pyrazole compounds: 3,5-dimethylpyrazole, 3-methylpyrazole, 4-bromo-3,5-dimethylpyrazole, 4-nitro-3,5-dimethylpyrazole, etc.
Active methylene type: Malonic acid diester (dimethyl malonate, diethyl malonate, di-n-butyl malonate, di-2-ethylhexyl malonate) and the like.
Triazole compounds: 1,2,4-triazole and the like. Of these, pyrazole compounds are preferred from the viewpoints of heat and humidity resistance and yellowing.

  The polyisocyanate which is the precursor of the blocked isocyanate of the present invention is obtained by introducing diisocyanate. Examples thereof include 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' -diisocyanate, aromatic aliphatic diisocyanates such as xylylene diisocyanate, alicyclic diisocyanates such as isophorone diisocyanate and 4,4-dicyclohexylmethane diisocyanate, 1,3-bis (isocyanatomethyl) cyclohexane , Hexamethylene diisocyanate, and aliphatic diisocyanates such as 2,2,4-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 agent etc., and adhesiveness may fall.

  The blocked isocyanate of the present invention can introduce a hydrophilic group into the polyisocyanate which is a precursor 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 Examples thereof include polyethylene glycol and polypropylene glycol blocked at one end. When a hydrophilic site is introduced, it becomes (1) cationic, (2) anionic, and (3) nonionic. Especially, since many other water-soluble resins are anionic, the anionic property and nonionic property which can be easily compatible are preferable. In addition, anionic properties are excellent in compatibility with other resins, and nonionic properties are preferred for improving heat and moisture resistance because they have no ionic hydrophilic groups. In addition, anionic and cationic ones aggregate with other resins or self-aggregate, which may affect 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 preferred. 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. For example, ammonia, methylamine, ethylamine, propylamine, isopropylamine, butylamine, 2-ethylhexylamine, cyclohexylamine, dimethylamine, diethylamine, dipropylamine, diisopropylamine, dibutylamine, trimethylamine, triethylamine, triisopropylamine, tributylamine , Linear, branched 1, 2 or tertiary amines having 1 to 20 carbon atoms such as ethylenediamine, morpholine, N-alkylmorpholine, cyclic amines such as pyridine, monoisopropanolamine, methylethanolamine, methylisopropanolamine, Dimethylethanolamine, diisopropanolamine, diethanolamine, triethanolamine, diethylethanolamine, triethanol A hydroxyl group-containing amines such as triethanolamine and the like.

  The nonionic hydrophilic group is preferably 3 to 50, more preferably 5 to 30, of ethylene glycol and polypropylene oxide ethylene oxide and / or propylene oxide capped at one end with an alkoxy group. 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 water dispersibility, the non-ionic, anionic, cationic and amphoteric surfactants can be added to the blocked isocyanate of the present invention. For example, nonionics such as polyethylene glycol and polyhydric alcohol fatty acid esters, fatty acid salts, alkyl sulfates, alkylbenzene sulfonates, sulfosuccinates, alkyl phosphates and other anionic systems, alkylamine salts, cationic systems such as alkyl betaines, Examples thereof include surfactants such as carboxylic acid amine salts, sulfonic acid amine salts, and sulfate ester salts.

  In addition to water, a water-soluble organic solvent can be contained. 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 layer is preferably 1/9 to 9/1, more preferably 1/9 to 8/2, and more preferably 2/8 to 6/4. Further preferred. Moreover, as content of the block isocyanate in the solid component of an application layer, 5 mass% or more and 90 mass% or less are preferable. More preferably, it is 20 mass% or more and 80 mass% or less. When the amount is small, the solvent resistance of the coating layer is reduced, and the adhesiveness under high temperature and high humidity is reduced.When the amount is large, the flexibility of the resin of the coating layer is reduced, and at room temperature and high temperature and high humidity. The adhesiveness of is reduced. 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 coating film strength. 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 liquid and the effect of improving 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. 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, silicic acid Inorganic particles such as aluminum, 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 size of 1 to 500 nm. Although an average particle diameter is not specifically limited, If it is 1-100 nm from the point which maintains the transparency of a film, it is preferable.

  The particles may contain two or more kinds of particles having different average particle diameters.

  In addition, said average particle diameter measures the maximum diameter of the 10 or more particle | grains which exist in the cross section of a coating layer by image | photographing the cross section of a laminated film at a magnification of 120,000 times using a transmission electron microscope (TEM). And can be obtained as an average value of them.

  As content of particle | grains, 0.5 mass% or more and 20 mass% or less are preferable. When the amount is small, sufficient blocking resistance cannot be obtained. Further, 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 and nonionic surfactants, 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 adhesiveness 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, examples of the method for providing the coating layer on the polyester film include a method in which a coating solution containing a solvent, particles and a resin is applied to the polyester film and dried. 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.

(Manufacture of easily adhesive polyester film for solar cells)
The method for producing an optically easy-adhesive polyester film of the present invention will be described using a polyethylene terephthalate (hereinafter abbreviated as PET) film as an example, but is not limited to this.

  The coating layer is formed by coating a coating solution on at least one surface of a PET film at any stage of the formed film or film manufacturing process. In particular, coating (in-line coating method) in a film-making increase 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 PET film. The solid content concentration of the resin composition in the coating solution is preferably 2 to 35% by weight, particularly preferably 4 to 15% by weight.

  Any known method can be used as a method for applying the coating solution to the PET 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 PET film, drying it, stretching it at least in a uniaxial direction, and then performing a heat treatment.

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

  The film used as the substrate can be obtained as follows, taking a PET film as an example. After sufficiently drying the PET resin in a vacuum, it is supplied to an extruder, melted and extruded at about 280 ° C. from a T-die into a rotating cooling roll into a sheet, cooled and solidified by an electrostatic application method, and unstretched PET. Get a sheet. The unstretched PET sheet may have a single layer structure or a multilayer structure by a coextrusion method. Moreover, it is preferable not to contain an inert particle substantially in PET resin.

  The obtained unstretched PET sheet is stretched 2.5 to 5.0 times in the longitudinal direction with a roll heated to 80 to 120 ° C. to obtain a uniaxially stretched PET film. Furthermore, the edge part of a film is hold | gripped with a clip, it guide | induces to the hot-air zone in the tenter heated at 70-140 degreeC, and is extended | stretched 2.5 to 5.0 times in the width direction, and is set to the heat processing zone in a tenter. Guidance and heat treatment. In order that the blocking agent of the present invention is suitably dissociated by heat addition, the maximum temperature in the tenter and the heat treatment time during heat treatment are preferably 160 ° C. or higher and 1 second or longer, and 180 ° C. or higher and 5 seconds or longer. More preferred. 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.

(Front sheet for solar cells)
The front sheet for a solar cell of the present invention comprises a polyester film having the coating layer 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 solar cell backsheet of the present invention can exhibit strong adhesion to the encapsulant, and can exhibit good adhesion even under harsh environments 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, polyester film having the coating layer / adhesive / film having a metal-based thin film layer / adhesive / hard coat layer, or polyester having the coating layer Examples of the configuration include a film / adhesive / hard coat layer. Further, the polyester film of the present invention may have a configuration having the coating layer on both sides. In this case, the lamination process can be suitably performed without newly providing an adhesive layer. The coating layer of the present invention 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 preferred embodiment 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 embodiment for 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 this invention can be used suitably also as an innermost layer (layer on the side in contact with the sealing agent) of the solar cell backsheet.

(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 sealant, 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 sealant is contained. For example, a crosslinking agent or a reaction initiator for causing the crosslinking reaction to proceed is added. For example, when thermal crosslinking is performed, 2,5-dimethylhexane-2,5-dihydroxyperoxide, 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne-3, di-t Organic peroxides such as -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. It may be blended for the purpose of promoting adhesion and curing, and the epoxy group-containing compound includes triglycidyl tris (2-hydroxyethyl) isocyanurate, neopentyl glycol diglycidyl ether, 1,6-hexanediol. Epoxy group-containing compounds such as diglycidyl ether, acrylic glycidyl ether, and 2-ethylhexyl glycidyl ether are used.

EXAMPLES Next, although this invention is demonstrated in detail using an Example , a reference example, and a comparative example, this invention is naturally not limited to a following example. The evaluation method used in the present invention is as follows.

(1) Intrinsic viscosity Based on JIS K7367-5, it measured at 30 degreeC, using the mixed solvent of phenol (60 mass%) and 1,1,2,2-tetrachloroethane (40 mass%) as a solvent.

(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 Inc. make, DSC6200).

(3) Absorbance measurement by infrared spectroscopy About the obtained easily adhesive polyester film for solar cells, the coating layer was scraped off and about 1 mg of a sample 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 spectrum of the coating layer was determined as the 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 SPECTRA TECH IRμs / SIRM
Detector: MCT
Resolution: 4cm ^-1
Integration count: 128 times

(4) Adhesiveness The prepared easy-adhesive polyester film for solar cells was cut into 100 mm width × 100 mm length, and the EVA sheet was cut into 70 mm width × 90 mm length, and the film (coating layer surface) / EVA / (described below) Coating layer surface) A sample was prepared by stacking with a film configuration and thermocompression bonding with a vacuum laminator under the adhesion conditions described below. The prepared sample was cut out into a width of 20 mm and a length of 100 mm, 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 portions that peeled stably after exceeding the maximum point. The ranking was based on the following criteria.
◎: 100 N / 20 mm or more, or film breakage of film ○: 75 N / 20 mm or more, less than 100 N / 20 mm Δ: 50 N / 20 mm or more, less than 75 N / 20 mm ×: less than 50 N / 20 mm

(Sample creation conditions)
Apparatus: Vacuum laminator NP-30 type LM-30x30 pressurization: 1 atmosphere EVA:
A. Standard cure type 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)
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 Sunvik Ultra Pearl PV (0.45μm)
Lamination process: 135 ° C (vacuum 5 minutes, vacuum pressure 15 minutes)
II. Mitsui Fabro Solar Eva RC02B (0.45μm)
Lamination process: 150 ° C. (vacuum 5 minutes, vacuum pressure 15 minutes)

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

(5) Moisture and heat resistance The obtained easily adhesive polyester film for solar cells was left in an environment of 85 ° C. and 85% RH for 1000 hours in a high-temperature and high-humidity tank. Next, the polyester film for solar cells 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 (4) above, and ranked according to the following criteria.
◎: 100 N / 20 mm or more, or film breakage of film ○: 75 N / 20 mm or more, less than 100 N / 20 mm Δ: 50 N / 20 mm or more, less than 75 N / 20 mm ×: less than 50 N / 20 mm

(6) Haze The haze of the obtained easily adhesive polyester film for solar cells was measured using a turbidimeter (Nippon Denshoku, NDH2000) based on JIS K7136.

(Polymerization of urethane resin A-1 containing aliphatic polycarbonate polyol)
In a four-necked flask equipped with a stirrer, a Dimroth condenser, a nitrogen inlet tube, a silica gel drying tube, and a thermometer, 43.75 parts by mass of 4,4-dicyclohexylmethane 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 were added and stirred at 75 ° C. for 3 hours in a nitrogen atmosphere. It was confirmed that the liquid 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 and adjusted to 25 ° C., while stirring and mixing 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%. The obtained polyurethane resin (A-1) had a glass transition temperature of -30 ° C.

(Polymerization of urethane resin A-2 containing aliphatic polycarbonate polyol)
In a four-necked flask equipped with a stirrer, a Dimroth condenser, a nitrogen inlet tube, a silica gel drying tube, and a thermometer, 29.14 parts by mass of 4,4-dicyclohexylmethane diisocyanate, 7.57 parts by mass of dimethylolbutanoic acid, A polyhexamethylene carbonate diol having a number average molecular weight of 3000, 173.29 parts by mass, 0.03 parts by mass of dibutyltin dilaurate, and 84.00 parts by mass of acetone as a solvent were added, and the mixture was stirred at 75 ° C. for 3 hours in a nitrogen atmosphere. It was confirmed that the liquid 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 and adjusted to 25 ° C., while stirring and mixing 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%.

(Polymerization of urethane resin A-3 containing aliphatic polycarbonate polyol as a constituent)
In a four-necked flask equipped with a stirrer, a Dimroth condenser, a nitrogen inlet tube, a silica gel drying tube, and a thermometer, 43.75 parts by mass of 4,4-dicyclohexylmethane diisocyanate, 11.12 parts by mass of dimethylolbutanoic acid, 1.97 parts by mass of hexanediol, 143.40 parts by mass of polyhexamethylene carbonate diol having a number average molecular weight of 2,000, 0.03 parts by mass of dibutyltin dilaurate, and 84.00 parts by mass of acetone as a solvent were added. The mixture was stirred at 0 ° C. for 3 hours, and it was confirmed 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 and adjusted to 25 ° C., while stirring and mixing 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%.

(Polymerization of urethane resin A-5 containing aliphatic polycarbonate polyol as a constituent)
A water-soluble polyurethane resin having a solid content of 35% was obtained in the same manner except that the polyhexamethylene carbonate diol having a number average molecular weight of 2000 in the water-soluble polyurethane resin (A-1) was changed to a polyhexamethylene carbonate diol having a number average molecular weight of 1000. A solution (A-5) was obtained.

(Polymerization of urethane resin A-6 containing aliphatic polycarbonate polyol as a constituent)
A water-soluble polyurethane resin having a solid content of 35% was obtained in the same manner except that the polyhexamethylene carbonate diol having a number average molecular weight of 2000 in the water-soluble polyurethane resin (A-1) was changed to a polyhexamethylene carbonate diol having a number average molecular weight of 5000. A solution (A-6) was obtained.

(Polymerization A-7 of Polyurethane Resin Containing Polyester Polyol)
A water-soluble polyurethane resin solution (A) having a solid content of 35% was obtained in the same manner except that the polyhexamethylene carbonate diol having a number average molecular weight of 2000 of the water-soluble polyurethane resin (A-1) was changed to a polyester diol having a number average molecular weight of 2000. -7) was obtained.

(Polymerization of block polyisocyanate crosslinking agent B-1)
A flask equipped with a stirrer, thermometer, reflux condenser, and polyisocyanate compound having an isocyanurate structure using hexamethylene diisocyanate as a raw material (manufactured by Asahi Kasei Chemicals, Duranate TPA) with 52.21 parts by mass of polyethylene glycol monomethyl ether (average molecular weight) 1000) 20.72 parts by mass were added dropwise and kept at 70 ° C. for 5 hours under an 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.

(Polymerization of block polyisocyanate crosslinking agent B-2)
A flask equipped with a stirrer, thermometer, reflux condenser, and polyisocyanate compound having a biuret structure made of hexamethylene diisocyanate as a raw material (manufactured by Asahi Kasei Chemicals, Duranate 24A-100), 52.54 parts by mass, polyethylene glycol monomethyl ether (average) (Molecular weight 1000) 19.78 mass parts It hold | maintained at 70 degreeC under the elementary atmosphere for 5 hours. 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.

(Polymerization of block polyisocyanate crosslinking agent B-3)
A polyisocyanate compound having an isocyanurate structure using hexamethylene diisocyanate as a raw material in a flask equipped with a stirrer, thermometer, and reflux condenser (66,04 parts by mass, manufactured by Asahi Kasei Chemicals, Duranate TPA), 17.50 N-methylpyrrolidone 25.19 parts by mass of 3,5-dimethylpyrazole (dissociation temperature: 120 ° C., boiling point: 218 ° C.) was added dropwise to parts by mass, and the mixture was held at 70 ° C. for 1 hour in an atmosphere of 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.

(Polymerization of block polyisocyanate crosslinking agent B-4)
Except for changing 3,5-dimethylpyrazole (dissociation temperature: 120 ° C., boiling point: 218 ° C.) of the block polyisocyanate aqueous dispersion (B-1) to diethyl malonate (dissociation temperature: 120 ° C., boiling point 199 ° C.). In the same manner, a block polyisocyanate aqueous dispersion (B-4) having a solid content of 40% was obtained.

(Polymerization of block polyisocyanate crosslinking agent B-5)
Except for changing 3,5-dimethylpyrazole (dissociation temperature: 120 ° C., boiling point: 218 ° C.) of the block polyisocyanate aqueous dispersion (B-1) to methyl ethyl ketoxime (dissociation temperature: 140 ° C., boiling point: 152 ° C.). In the same manner, a block polyisocyanate aqueous dispersion (B-5) having a solid content of 40% was obtained.

(Polymerization of block polyisocyanate crosslinking agent B-6)
Except for changing 3,5-dimethylpyrazole (dissociation temperature: 120 ° C., boiling point: 218 ° C.) of the block polyisocyanate aqueous dispersion (B-3) to methyl ethyl ketoxime (dissociation temperature: 140 ° C., boiling point: 152 ° C.). A block polyisocyanate aqueous dispersion (B-6) having a solid content of 40% was obtained in the same manner.

Reference example 1
(1) Adjustment of coating liquid The following coating agent was mixed and the coating liquid was created.
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 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) Manufacture of an easy-adhesive polyester film for solar cells PET resin pellets having an intrinsic viscosity of 0.69 g / dl, which practically do not contain particles, are dried under reduced pressure at 135 ° C. for 6 hours (1 Torr). After that, PET resin having an intrinsic viscosity of 0.69 g / dl, in which porous silica having an average particle size of 2.5 μm (electron microscopic method) is blended in the extruder 2 (for the intermediate layer) so as to have a concentration of 0.06% by mass. Were respectively supplied to the extruder 1 (for outer layer) and melted at 285 ° C. These two polymers were laminated in a three-layer merge block, extruded into a sheet form from a die, wound around a casting drum having a surface temperature of 30 ° C., and cooled and solidified to form an unstretched film. At this time, the discharge amount of each extruder was adjusted so that the thickness ratio of the A layer, the B layer, and the C layer was 1.5: 7: 1.5.

  This unstretched PET sheet was heated to 100 ° C. with a heated roll group and an infrared heater, and then stretched 3.5 times in the longitudinal direction with a roll group having a difference in peripheral speed to obtain a uniaxially stretched PET film.

Next, the coating solution which was allowed to stand for 5 hours or more at room temperature was applied to one side of a PET film by a roll coating method, and then dried at 80 ° C. for 20 seconds. The final coating amount after drying (after biaxial stretching) was adjusted to 0.15 g / m ² (the coating layer thickness after drying was 150 nm). Subsequently, the film was stretched 4.0 times in the width direction at 120 ° C. with a tenter, and heated at 230 ° C. for 0.5 seconds with the length in the width direction fixed, and further at 100 ° C. for 10 seconds for 3 seconds. % Relaxation treatment in the width direction was performed to obtain a 100 μm easily adhesive polyester film for solar cells. The evaluation results are shown in Table 1.

Comparative Example 1
A solar cell easy-adhesive polyester film was obtained in the same manner as in Reference Example 1 except that the block polyisocyanate aqueous dispersion was changed to the block polyisocyanate aqueous dispersion (B-5).

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

Comparative Example 3
Easy adhesion for solar cells in the same manner as in Reference Example 1 except that the block polyisocyanate aqueous dispersion was changed to a polyisocyanate aqueous dispersion having an isocyanurate structure made from hexamethylene diisocyanate (WT30-100 manufactured by Asahi Kasei Chemicals). A polyester film was obtained.

Reference example 2
Except having changed the coating liquid into the following, it carried out similarly to the reference example 1, 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)

Reference example 3
Except having changed the coating liquid into the following, it carried out similarly to the reference example 1, 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)

Example 4
Except having changed the coating liquid into the following, it carried out similarly to the reference example 1, 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)

Example 5
Except having changed the coating liquid into the following, it carried out similarly to the reference 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)

Example 6
Except having changed the coating liquid into the following, it carried out similarly to the reference example 1, 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)

Reference Example 7
Except having changed the polyurethane resin into the polyurethane resin (A-2), it carried out similarly to the reference example 1, and obtained the easily adhesive polyester film for solar cells.

Reference Example 8
Except having changed the polyurethane resin into the polyurethane resin (A-3), it carried out similarly to the reference example 1, and obtained the easily adhesive polyester film for solar cells.

Reference Example 9
An easily adhesive polyester film for solar cells was obtained in the same manner as in Reference Example 1 except that the polyurethane resin was changed to the polyurethane resin (A-5).

Reference Example 10
A reester film for a solar cell was obtained in the same manner as in Reference Example 1 except that the polyurethane resin was changed to the polyurethane resin (A-6).

Reference Example 11
Except having changed the polyurethane resin into the polyurethane resin (A-7), it carried out similarly to the reference example 1, and obtained the easily adhesive polyester film for solar cells.

Reference Example 12
An easily adhesive polyester film for solar cells was obtained in the same manner as in Reference Example 1 except that the block polyisocyanate aqueous dispersion (B-1) was changed to the block polyisocyanate aqueous dispersion (B-2).

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

Reference Example 14
An easily adhesive polyester film for solar cells was obtained in the same manner as in Reference Example 1 except that the block polyisocyanate aqueous dispersion (B-1) was changed to the block polyisocyanate aqueous dispersion (B-4).

Reference Example 15
An easy-adhesive polyester film for solar cells was obtained in the same manner as in Reference Example 1 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.

Reference Example 16
An easy-adhesive polyester film for solar cells was obtained in the same manner as in Reference Example 1 except that the substrate thickness of the easy-adhesive polyester film for solar cells was changed to 50 μm.

Reference Example 17
A solar cell easy-adhesive polyester film was obtained in the same manner as in Reference Example 15 except that the substrate thickness of the solar cell easy-adhesive polyester film was changed to 350 μm.

Reference Example 18
An easy-adhesive polyester film for solar cells was obtained in the same manner as in Reference Example 16 except that the coating solution was changed to the following.
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 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)

Reference Example 19
Except having changed the coating liquid into the following, it carried out similarly to the reference example 1, 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)

Reference Example 20
(3) Manufacture of front sheets for solar cells
A solar cell easy-adhesive polyester film was obtained in the same manner as in Reference Example 1 except that coating layers were formed on both sides 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).

  Since the easily adhesive polyester film for solar cells of the present invention is excellent in transparency and adhesiveness, it is suitable as a base film for a solar cell front sheet.

Claims (4)

A polyester film having a coating layer on at least one side,
The coating layer is mainly composed of urethane resin and blocked isocyanate,
The mass ratio of urethane resin and blocked isocyanate (urethane resin / block isocyanate) in the coating layer is 1/9 to 8/2,
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.   The easily adhesive polyester film for solar cells according to claim 1, wherein the urethane resin is a urethane resin containing an aliphatic polycarbonate polyol as a constituent component. Ratio (A ₁₄₆₀ ) of the absorbance at the peak near 1460 cm ⁻¹ derived from the aliphatic polycarbonate component (A ₁₄₆₀ ) and the absorbance at the peak near 1530 cm ⁻¹ derived from the urethane component (A ₁₅₃₀ ) in the infrared spectrum of the coating layer (A ₁₄₆₀ / _{a 1530)} is 0.50 to 1.55, highly adhesive polyester film for a solar cell according to claim 2. The solar cell front sheet which laminated | stacked the easily adhesive polyester film for solar cells in any one of Claims 1-3 .