JP4803317B2 - Easy-adhesive polyester film for solar cell and back sheet using the same - Google Patents

Description

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

  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.

  As a solar cell backsheet, from the solar cell element side (encapsulant side) to polyester film / adhesive / polyester film (colored) / metal or metal oxide thin film layer (moisture-proof layer) / adhesive / fluorine Those having a laminated structure such as a film (antifouling layer) have been proposed. The backsheet serves to protect the solar cell element from external moisture and contamination over a long period of time. Therefore, the adhesiveness between the sealing material and the polyester film on the solar cell element side that is in direct contact with the sealing material is important. 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 1 to 4).

JP 2006-152013 A JP 2006-320991 A JP 2007-48944 A JP 2007-136911 A

  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, the easy-adhesive polyester film for solar cells as disclosed in the above patent document still has insufficient adhesiveness, and a decrease in adhesive strength is unavoidable particularly in long-term use under high temperature and high humidity. It was a thing.

  In addition, various composition types including additives such as a crosslinking agent and an ultraviolet absorber have come to be used for the sealing material from the viewpoint of improving productivity and preventing deterioration. Also, various packaging processes have been adopted depending on the sealing material used. 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, there is a demand for a highly versatile and easy-to-adhere film that can cope with various bonding conditions as well as high versatility that exhibits the same level of adhesion to various sealing materials.

  In view of the above problems, the present invention has strong adhesiveness that can withstand harsh environments, hardly causes deterioration of adhesiveness under high temperature and high humidity, which has been conventionally considered to be unavoidable, and has various sealing properties. It is an object of the present invention to provide an easily adhesive polyester film for solar cells that has good adhesion to a stopper.

As a result of intensive studies to solve the above problems, the present inventor has found that a polyester film having a coating layer on at least one surface, the main component is a urethane resin having an aliphatic polycarbonate polyol as a constituent component, and infrared spectroscopy. In the spectrum, the ratio (A ₁₄₆₀ / A ₁₅₃₀ ) of the absorbance (A ₁₄₆₀ ) near 1460 cm ⁻¹ derived from the aliphatic polycarbonate component to the absorbance (A ₁₅₃₀ ) near 1530 cm ⁻¹ derived from the urethane component is 0.50 to 1 .55 is a coating layer that provides strong adhesiveness that can withstand harsh environments even when using various sealing materials and bonding conditions, and has excellent adhesiveness even under high temperature and high humidity conditions. As a result, the present invention has been found.

The above-described problem can be achieved by the following solution means.
(1) A polyester film having a coating layer on at least one side and having a substrate thickness of 20 μm to 500 μm, wherein the coating layer is mainly composed of a urethane resin having an aliphatic polycarbonate polyol as a constituent component and a crosslinking agent, The ratio (A ₁₄₆₀ / A ₁₅₃₀ ) of the absorbance (A ₁₄₆₀ ) near 1460 cm ⁻¹ derived from the aliphatic polycarbonate component and the absorbance (A ₁₅₃₀ ) near 1530 cm ⁻¹ derived from the urethane component in the infrared spectrum of the coating layer. ) Is 0.50 to 1.55, an easily adhesive polyester film for solar cells.
(2) The solar cell easily adhesive polyester film, wherein the crosslinking agent is at least one crosslinking agent selected from a melamine crosslinking agent, an isocyanate crosslinking agent, a carbodiimide crosslinking agent, and an oxazoline crosslinking agent.
(3) The said easily adhesive polyester film for solar cells whose content of the said crosslinking agent in the said application layer is 5 to 90 mass% with respect to urethane resin.
(4) The said easily adhesive polyester film for solar cells whose number average molecular weights of the said aliphatic polycarbonate polyol are 1500-4000.
(5) The urethane resin contains an aliphatic polycarbonate polyol, a polyisocyanate, and a chain extender as components, and the chain extender is an aliphatic diol having 4 to 10 carbon atoms or an aliphatic having 4 to 10 carbon atoms. The easily adhesive polyester film for solar cells, which is a diamine.
(6) The said easily adhesive polyester film for solar cells whose crow transition point temperature of the said urethane resin is less than 0 degreeC.
(7) The said easily adhesive polyester film for solar cells in which the said urethane resin contains 3-60 mol% of polyol which has a carboxylic acid group or a carboxylate group as a structural component in all the polyisocyanates.
(8) The easy-adhesive polyester film for solar cells, which is used for laminating a sealing material mainly composed of an ethylene vinyl acetate copolymer or a polyvinyl butyral resin.
(9) A solar cell backsheet in which the easily adhesive polyester film for solar cells is laminated on the outermost layer .
( 10) A solar cell module obtained by laminating a sealing material on the coating layer surface of the solar cell backsheet.

  The easily-adhesive polyester film for solar cells of the present invention exhibits strong adhesion even under various sealing materials and adhesion conditions, and is particularly excellent in adhesion (humidity heat resistance) under high temperature and high humidity. Therefore, as a preferred embodiment, the adhesiveness at the high temperature and high humidity treatment is maintained at the same level as the initial adhesiveness. 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 back sheet, the adhesiveness with a sealing material is good.

(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.

  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 the case of a three-layer structure in the present invention, particles are contained in the outermost layer (A layer in the case of the above-mentioned two types and three layers), and particles are substantially contained in the central layer (B layer in the case of the above two types and three layers) May not be included. The reason why it is preferable to include particles in the A layer is that when the polyester film of the present invention is used as a member for a solar cell, a metal or a moisture-proof functional layer such as a metal oxide thin film layer or a coating layer, This is for improving the handling property in the post-processing step such as laminating a fouling functional layer. When particles are added to the outermost layer, sufficient handling properties suitable for processability can be obtained.

  The reason why it is preferable that the B layer substantially does not contain particles is to reduce the probability of formation of protrusions due to aggregates of lubricant particles, particularly inorganic particles. Further, by adopting such a configuration, a highly transparent film can be obtained, which is suitable for a field requiring transparency, such as a see-through solar cell.

  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.

  These layers may contain various additives in the polyester as necessary. Examples of the additive include an antioxidant, a light resistance agent, an antigelling agent, an organic wetting agent, an antistatic agent, an ultraviolet absorber, and a surfactant.

  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.

  As a method of blending the above particles with polyester, a known method can be adopted. 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.

  The thickness of the polyester film used as the base material of the present invention is 20 to 500 μm, more preferably 25 to 450 μm, and still more preferably 30 to 300 μm. 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.

(Coating layer)
In the easily adhesive polyester film for solar cells of the present invention, a coating layer mainly composed of a urethane resin having a aliphatic polycarbonate polyol as a constituent component and a crosslinking agent is formed, and an aliphatic layer is measured by infrared spectroscopy. The ratio (A ₁₄₆₀ / A ₁₅₃₀ ) of the absorbance (A ₁₄₆₀ ) near 1460 cm ⁻¹ derived from the polycarbonate-based polycarbonate component to the absorbance (A ₁₅₃₀ ) near 1530 cm ⁻¹ derived from the urethane component is 0.50 to 1.55. This is very important. 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 the total solid component contained in the coating layer.

  As in the above Patent Documents 2 to 5, it is desirable that the conventional technical common sense positively introduces a cross-linking structure in the formation of the coating layer in order to improve the durability of the coating layer, thereby forming a rigid and strong coating layer. It was thought. 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. As a result, the inventors have found a remarkable effect of improving the quality of the present invention and have reached the present invention. 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 present invention, the coating layer is mainly composed of a urethane resin having an aliphatic polycarbonate polyol as a constituent component and a cross-linking agent as a main component, and the coating layer is in the vicinity of 1460 cm ⁻¹ derived from an aliphatic polycarbonate component measured by infrared spectroscopy. _{By making} the ratio (A ₁₄₆₀ / A ₁₅₃₀ ) of the absorbance (A ₁₄₆₀ ) and the absorbance (A ₁₅₃₀ ) in the vicinity of 1530 cm ⁻¹ derived from the urethane component 0.50 to 1.55, the above characteristics can be 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 0.50 to 1.55, but the lower limit of the ratio (A ₁₄₆₀ / A ₁₅₃₀ ) is preferably 0.60, more preferably 0.00. 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 moisture resistance is 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. Decreases.

  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. In this invention, it has an aliphatic polycarbonate polyol as a structural component of a urethane resin. Heat-moisture resistance can be improved by including a urethane resin containing an aliphatic polycarbonate polyol as a constituent component in the coating layer of the present invention. The components of these urethane resins can be specified by nuclear magnetic resonance analysis or the like.

  The diol component, which is a constituent component of the urethane resin of the present invention, needs to contain an aliphatic polycarbonate polyol having excellent heat resistance and hydrolysis resistance. From the viewpoint of preventing yellowing by sunlight of the present invention, it is preferable to use an aliphatic polycarbonate polyol.

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.

(Additive)
In the present invention, the coating layer must contain a crosslinking agent. By including a crosslinking agent, it becomes possible to further improve the adhesiveness under high temperature and high humidity. Moreover, when making it heat-press by high temperature for a short time, the fall of the base-material adhesiveness by EVA erosion can be prevented. Therefore, highly versatile and easy-to-adhere that can be applied under various bonding conditions. As the crosslinking agent, those that react with a carboxylic acid group, a hydroxyl group, an amino group, etc. to form an amide bond, a urethane bond, or a urea bond are preferable because they are not easily deteriorated by high-temperature and high-humidity treatment. Conversely, when an ester bond or an ether bond is involved, it may be hydrolyzable, which is not preferable. Examples of the crosslinking agent suitably used in the present invention include melamine-based, isocyanate-based, carbodiimide-based, and oxazoline-based. Among these, an isocyanate type and a carbodiimide type are preferable from the viewpoint of the stability over time of the coating liquid and the effect of improving the adhesiveness under high temperature and high humidity treatment. Furthermore, it is particularly preferable to use an isocyanate-based crosslinking agent from the viewpoint that the coating layer has appropriate flexibility and suitably imparts the stress relaxation action of the coating layer. Moreover, in order to promote a crosslinking reaction, a catalyst etc. are used suitably as needed.

  As content of a crosslinking agent, 5 mass% or more and 90 mass% or less are preferable with respect to a urethane resin. More preferably, it is 10 mass% or more and 50 mass% or less. If the amount is small, the strength of the coating layer under high temperature and high humidity may decrease, and the adhesiveness may decrease. Adhesiveness may be reduced.

  In the present invention, two kinds of crosslinking agents may be mixed in order to improve the coating film strength. Moreover, in order to promote a crosslinking reaction, a catalyst etc. are used suitably as needed.

  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, satin white, aluminum silicate, diatomaceous earth Inorganic particles such as soil, 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, phenol, di Rirufutareto systems include organic particles of 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.

  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 heated at 70-140 degreeC, and is extended | stretched 2.5 to 5.0 times in the width direction. Then, it guide | induces to the heat processing zone of 160-240 degreeC, and heat-processes for 1 to 60 seconds, and completes crystal orientation.

  In an arbitrary stage of the film manufacturing process, a coating solution is applied to at least one surface of the PET film to form the coating layer. 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 present invention, the coating layer is formed by coating the coating solution on an unstretched or uniaxially stretched PET film, drying it, stretching in at least a uniaxial direction, and then performing a heat treatment. Since the adhesion between the coating layer and the polyester film substrate is further improved by the in-line coating method for forming the coating layer during film formation, it is preferable in terms of improving the adhesion with the sealing material after high temperature and high humidity. In addition, it is preferable to apply a high-temperature heat treatment to the coating layer in that a cross-linking agent contained in the coating layer reacts to form a more suitable coating layer due to moisture and heat resistance.

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.

(Back sheet for solar cell)
The back sheet for 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 back sheet for solar cells of the present invention, for example, a polyester film / adhesive / metal foil having a coating layer or a film / adhesive / polyvinyl fluoride film having a metal-based thin film layer or a polyester-based highly durable moisture-proof A configuration such as a film is exemplified. Further, the polyester film of the present invention may have a configuration having the coating layer on both sides. 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.

  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.

  In the present invention, each layer of the polyester film having the coating layer, the metal foil or the metal-based thin film layer, the polyvinyl fluoride film or the polyester-based high durability moisture-proof film is integrally laminated by vacuum suction or the like and heat-pressed. The solar cell backsheet can be produced by thermocompression-molding each of the above-mentioned layers as an integrally molded body using a normal molding method such as the cation method. In the above, in order to improve the adhesiveness etc. between each film, it is preferable to laminate | stack via an adhesive agent. Examples of the adhesive include (meth) acrylic resins, olefinic resins, vinyl resins, and other heat melting adhesives, solvent-based adhesives, photo-curing adhesives, etc. whose main component is a vehicle. It is done.

  Here, the high durability moisture-proof film is laminated for the purpose of improving the weather resistance. Examples of the high durability moisture-proof film include polytetrafluoroethylene (PTFE), 4-fluoroethylene-perchloroalkoxy copolymer. Polymer (PFA), 4-Fluoroethylene-6-fluoropropylene copolymer (FEP), 2-Ethylene-4 fluoroethylene copolymer (ETFE), Poly-3-fluoroethylene (PCTFE), Polyfluoride Fluorine resin film such as vinylidene (PVDF) or polyfuca vinyl (PVF), or UV absorber for resin such as polycarbonate, polymethyl methacrylate, polyacrylate, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), acrylic A film made of a kneaded resin composition It is.

(Solar cell module)
The solar cell module uses, for example, a glass substrate, 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 backsheet of the present invention. Configured. 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 accelerating adhesion and curing. Examples of the epoxy group-containing compound include 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 and a comparative example, naturally this invention is 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

(Polymerization of urethane resin A-1 containing aliphatic polycarbonate polyol)
In a four-necked flask equipped with a stirrer, Dimroth cooler, nitrogen inlet tube, silica gel drying tube, and thermometer, 43.75 parts by mass of 4,4-diphenylmethane diisocyanate, 12.85 parts by mass of dimethylolbutanoic acid, several 153.41 parts by mass of polyhexamethylene carbonate diol having an 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 had reached the 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 added with an isocyanate group-terminated prepolymer while stirring and mixing at 2000 min ⁻¹ to disperse in water. did. 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 cooler, a nitrogen inlet tube, a silica gel drying tube, and a thermometer, 29.14 parts by mass of 4,4-diphenylmethane diisocyanate, 7.57 parts by mass of dimethylolbutanoic acid, several An average molecular weight of 3000 polyhexamethylene carbonate diol 173.29 parts by mass, dibutyltin dilaurate 0.03 parts by mass, 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 had reached the 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 added with an isocyanate group-terminated prepolymer while stirring and mixing at 2000 min ⁻¹ to disperse in water. did. 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, Dimroth cooler, nitrogen inlet tube, silica gel drying tube, and thermometer, 43.75 parts by mass of 4,4-diphenylmethane diisocyanate, 11.12 parts by mass of dimethylolbutanoic acid, hexane 1.97 parts by mass of diol, 143.40 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 75 ° C. in a nitrogen atmosphere. The mixture was stirred for 3 hours 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 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 silanol group-containing urethane resin A-4 containing aliphatic polycarbonate polyol as a constituent)
In a four-necked flask equipped with a stirrer, a Dimroth cooler, a nitrogen inlet tube, a silica gel drying tube, and a thermometer, 38.41 parts by mass of isophorone diisocyanate, 6.95 parts by mass of dimethylolpropanoic acid, and a number average molecular weight of 2000 Polyhexamethylene carbonate diol 158.999 parts by mass, dibutyltin dilaurate 0.03 parts by mass, and acetone 84.00 parts by mass as a solvent were added and stirred at 75 ° C. for 3 hours in a nitrogen atmosphere. It was confirmed that the equivalent amount was reached. Next, after cooling this reaction liquid to 40 degreeC, 4.37 mass parts of triethylamine was added, and the polyurethane prepolymer solution was obtained. Next, 3.84 parts by mass of γ- (aminoethyl) aminopropyltriethoxysilane and 1.80 parts by mass of 2-[(2-aminoethyl) amino] ethanol were added to 450 g of water, and the polyurethane prepolymer solution was added dropwise. And dispersed in water. Thereafter, a part of acetone and water was removed under reduced pressure to prepare a water-soluble silanol group-containing polyurethane resin solution (A-4) having a solid content of 30%.

(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 A-8 of Polyurethane Resin Containing Polyether Polyol)
A water-soluble polyurethane resin solution having a solid content of 35% (with a solid content of 35%), 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 polyether diol having a number average molecular weight of 2000. A-8) was obtained.

(Polymerization of urethane resin A-9 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, 32.39 parts by mass of 1,3-bis (isocyanatomethyl) cyclohexane, dimethylolbutanoic acid 13. 09 parts by mass, 156.74 parts by mass of polyhexamethylene carbonate diol having a number average molecular weight of 2000, 0.03 parts by mass of dibutyltin dilaurate, and 80.89 parts by mass of acetone as a solvent, and 3 hours at 75 ° C. in a nitrogen atmosphere The mixture was stirred 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-9) having a solid content of 35%. The obtained polyurethane resin (A-9) had a glass transition temperature of -30 ° C.

(Polymerization of urethane resin A-10 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, 45.93 parts by mass of 4,4-dicyclohexyl diisocyanate, 13.09 parts by mass of dimethylolbutanoic acid, several An average molecular weight of 3000 polyhexamethylene carbonate diol (235.11 parts by mass), dibutyltin dilaurate (0.03 parts by mass), and acetone (117.66 parts by mass) as a solvent were added, and the mixture was stirred at 75 ° C. for 3 hours in a nitrogen atmosphere. It was confirmed that had reached the 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-10) having a solid content of 35%. The obtained polyurethane resin (A-10) had a glass transition temperature of -40 ° C.

(Polymerization of block polyisocyanate crosslinking agent)
100 parts by mass of a polyisocyanate compound having an isocyanurate structure using hexamethylene diisocyanate as a raw material (manufactured by Asahi Kasei Chemicals, Duranate TPA) in a flask equipped with a stirrer, a thermometer and a reflux condenser, 55 parts by mass of propylene glycol monomethyl ether acetate, 30 parts by mass of polyethylene glycol monomethyl ether (average molecular weight 750) was charged and held at 70 ° C. for 4 hours in a nitrogen atmosphere. Thereafter, the reaction solution temperature was lowered to 50 ° C., and 47 parts by mass of methyl ethyl ketoxime was added dropwise. The infrared spectrum of the reaction solution was measured to confirm that the absorption of the isocyanate group had disappeared, and a block polyisocyanate aqueous dispersion (B) having a solid content of 75% by mass was obtained.

(Polymerization of oxazoline crosslinking agent)
A mixture of 58 parts by mass of ion-exchanged water and 58 parts by mass of isopropanol as an aqueous medium in a flask equipped with a thermometer, a nitrogen gas introduction tube, a reflux condenser, a dropping funnel, and a stirrer, and a polymerization initiator (2, 2 4 parts by mass of '-azobis (2-amidinopropane) dihydrochloride) was added. On the other hand, in a dropping funnel, 16 parts by mass of 2-isopropenyl-2-oxazoline as a polymerizable unsaturated monomer having an oxazoline group, methoxypolyethylene glycol acrylate (average number of moles of ethylene glycol added: 9 moles, Shin Nakamura Chemical) A mixture of 32 parts by mass and 32 parts by mass of methyl methacrylate was added, and the mixture was added dropwise at 70 ° C. for 1 hour in a nitrogen atmosphere. After completion of dropping, the reaction solution was stirred for 9 hours and cooled to obtain a water-soluble resin solution (C) having an oxazoline group having a solid content concentration of 40% by mass.

(Polymerization of carbodiimide crosslinking agent)
A flask equipped with a stirrer, thermometer and reflux condenser was charged with 168 parts by mass of hexamethylene diisocyanate and 220 parts by mass of polyethylene glycol monomethyl ether (M400, average molecular weight 400), stirred at 120 ° C. for 1 hour, 26 parts by mass of 4′-dicyclohexylmethane diisocyanate and 3.8 parts by mass of 3-methyl-1-phenyl-2-phospholene-1-oxide (2% by weight based on the total isocyanate) were added as a carbodiimidization catalyst, and 185 under a nitrogen stream. Stir at 5 ° C. for a further 5 hours. The infrared spectrum of the reaction solution was measured, and it was confirmed that absorption at a wavelength of 2200 to 2300 cm ⁻¹ disappeared. It stood to cool to 60 degreeC, 567 mass parts of ion-exchange water was added, and the carbodiimide water-soluble resin solution (D) of 40 mass% of solid content was obtained.

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) 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) Manufacture of easy-adhesive polyester film for solar cell A PET resin pellet (inherent viscosity is 0.62 dl / g) containing 0.03% by mass of silica particles having an average particle diameter of 2.5 μm as a film raw material polymer is 133 Pa. For 6 hours at 135 ° C. under reduced pressure. Then, it supplied to the extruder and melt | dissolved at about 285 degreeC. Each of the PET resins was filtered through a stainless steel filter medium (nominal filtration accuracy: 10 μm particle 95% cut) and melt extruded into a sheet. It was quenched and solidified on a rotating cooling metal roll maintained at a surface temperature of 30 ° C. to obtain an unstretched PET sheet.

  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.

Subsequently, after apply | coating the said coating liquid on the single side | surface of PET film by the roll coat method, it dried at 80 degreeC for 20 second. 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 250 μm easily adhesive polyester film for solar cells. The evaluation results are shown in Table 1.

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

Comparative Example 2
A solar cell reester film was obtained in the same manner as in Example 1 except that the polyurethane resin was changed to the polyurethane resin (A-6).

Comparative Example 3
Except having changed the polyurethane resin into the polyurethane resin (A-7), it carried out similarly to Example 1, and obtained the easily adhesive polyester film for solar cells.

Comparative Example 4
Except having changed the polyurethane resin into the polyurethane resin (A-8), it carried out similarly to Example 1, and obtained the easily adhesive polyester film for solar cells.

Comparative Example 5
A solar cell easy-adhesive polyester film was obtained in the same manner as in Example 1 except that the substrate thickness of the solar cell easy-adhesive polyester film was changed to 5 μm.

Example 2
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 58.02% by mass
Isopropanol 30.00% by mass
Polyurethane resin solution (A-1) 9.47% by mass
Block polyisocyanate aqueous dispersion (B) 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)

Example 3
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.
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) 1.52% 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 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) 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 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) 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 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) 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)

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

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

Example 9
An easily adhesive polyester film for solar cells was obtained in the same manner as in Example 1 except that the polyurethane resin was changed to a silanol group-containing polyurethane resin (A-4).

Example 10
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 (B) was changed to a water-soluble resin (C) having an oxazoline group.

Example 11
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 (C) was changed to the carbodiimide water-soluble resin (D).

Example 12
An easy-adhesive polyester film for solar cells was obtained in the same manner as in Example 1 except that the block polyisocyanate aqueous dispersion (C) was changed to imino / methylolmelamine (solid content concentration: 70% by mass).

Example 13
An easy-adhesive polyester film for solar cells was obtained in the same manner as in Example 1 except that the substrate thickness of the easy-adhesive polyester film for solar cells was changed to 50 μm.

Example 14
An easy-adhesive polyester film for solar cells was obtained in the same manner as in Example 1 except that the substrate thickness of the easy-adhesive polyester film for solar cells was changed to 100 μm.

Example 15
An easy-adhesive polyester film for solar cells was obtained in the same manner as in Example 1 except that the substrate thickness of the easy-adhesive polyester film for solar cells was changed to 350 μm.

Example 16
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.
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) 1.13% 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)

Example 17
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 45.9 mass%
Isopropanol 30.00% by mass
Polyurethane resin solution (A-1) 18.99% by mass
Block polyisocyanate aqueous dispersion (B) 3.80% by 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)

Example 18
(3) Manufacture of back sheet for solar cell By the dry lamination method with the structure of the easily adhesive polyester film for solar cells / black polyester film (50 μm) / aluminum foil (30 μm) / polyvinyl fluoride film (38 μm) of Example 1. The solar cell back sheet was obtained by bonding.
Adhesive for dry laminate Takelac A-315 (Mitsui Chemicals) / Takenate A-10 (Mitsui Chemicals) = 9/1 (solid content ratio)

Example 19
An easily adhesive polyester film for solar cells was obtained in the same manner as in Example 1 except that the polyurethane resin was changed to the polyurethane resin (A-9).

Example 20
Except having changed the polyurethane resin into the polyurethane resin (A-10), it carried out similarly to Example 1, and obtained the easily adhesive polyester film for solar cells.

Example 21
(3) Manufacture of solar cell backsheet A dry laminate method with a configuration of easy-adhesive polyester film for solar cell / black polyester film (50 μm) / aluminum foil (30 μm) / polyvinyl fluoride film (38 μm) in Example 19. The solar cell back sheet was obtained by bonding.
Adhesive for dry laminate Takelac A-315 (Mitsui Chemicals) / Takenate A-10 (Mitsui Chemicals) = 9/1 (solid content ratio)

Examples 22 and 23
In Example 18 and Example 21, a solar cell back sheet was prepared in the same manner except that a white polyester film (50 μm) was used instead of the black polyester film (50 μm). Example 22 using the easily adhesive polyester film for solar cells of Example 22 and Example 19 using the conductive polyester film was produced. About the obtained back sheet for solar cells, an I-super UV tester SUV-W151 manufactured by Iwasaki Electric Co., Ltd. was used with the easily adhesive polyester film surface for solar cells as an irradiation surface, and 63 ° C., 50% Rh, irradiation intensity 100 mW / cm ^2. And 100 hours of continuous UV irradiation treatment. As a result of visually confirming the solar cell backsheet after UV irradiation under a fluorescent lamp, the solar cell backsheet of Example 22 was slightly yellowed, but the solar cell backsheet of Example 23 was entirely exposed. There was no change in color, and a good appearance was maintained.

  The easily adhesive polyester film for solar cells of the present invention is excellent in adhesiveness under various sealing materials and adhesive conditions and adhesiveness under high temperature and high humidity (humidity heat resistance), so that it is the innermost interior of the backsheet for solar cells. It is suitable as a substrate film.

Claims (10)

It is a polyester film having a substrate thickness of 20 to 500 μm and having a coating layer on at least one side,
The coating layer is mainly composed of a urethane resin and a cross-linking agent having aliphatic polycarbonate polyol as constituent components,
The ratio (A ₁₄₆₀ / A ₁₅₃₀ ) of the absorbance (A ₁₄₆₀ ) near 1460 cm ⁻¹ derived from the aliphatic polycarbonate component and the absorbance (A ₁₅₃₀ ) near 1530 cm ⁻¹ derived from the urethane component in the infrared spectrum of the coating layer. ) Is 0.50 to 1.55, an easily adhesive polyester film for solar cells.   2. The solar cell according to claim 1, wherein the crosslinking agent is at least one crosslinking agent selected from a melamine crosslinking agent, an isocyanate crosslinking agent, a carbodiimide crosslinking agent, and an oxazoline crosslinking agent. Easy-adhesive polyester film.   The easily adhesive polyester film for solar cells according to claim 1 or 2, wherein the content of the crosslinking agent in the coating layer is 5% by mass or more and 90% by mass or less with respect to the urethane resin.   The easily adhesive polyester film for solar cells according to any one of claims 1 to 3, wherein the aliphatic polycarbonate polyol has a number average molecular weight of 1500 to 4000. The urethane resin contains aliphatic polycarbonate polyol, polyisocyanate, and chain extender as constituent components,
The easily adhesive polyester film for solar cells according to any one of claims 1 to 4, wherein the chain extender is an aliphatic diol having 4 to 10 carbon atoms or an aliphatic diamine having 4 to 10 carbon atoms. The easily adhesive polyester film for solar cells according to any one of claims 1 to 5, wherein the urethane resin has a glass transition temperature of less than 0 ° C.   The easily adhesive polyester film for solar cells according to any one of claims 1 to 6, wherein the urethane resin contains 3 to 60 mol% of a polyol having a carboxylic acid group or a carboxylic acid group as a constituent component in all polyisocyanates.   The easily adhesive polyester film for solar cells according to any one of claims 1 to 7, which is used for laminating a sealing material mainly composed of an ethylene vinyl acetate copolymer or a polyvinyl butyral resin.   The solar cell backsheet which laminated | stacked the easily adhesive polyester film for solar cells in any one of Claims 1-8 on the outermost layer.   The solar cell module formed by laminating | stacking a sealing material on the application layer surface of the solar cell backsheet described in Claim 9.