JP2016146378A - Backside protective sheet for solar cell module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a backside protective sheet for a solar cell module, which is excellent in scratch resistance.SOLUTION: The backside protective sheet for a solar cell module comprises at least a polyester film and an ultraviolet protective layer. The ultraviolet protective layer contains a resin component and inorganic particles. The light transmittance at 360 nm of the ultraviolet protective layer is 5% or less. The center surface average roughness of the ultraviolet protective layer is 0.05 to 0.12 μm inclusive.SELECTED DRAWING: None

Description

  The present invention relates to a back surface protection sheet for a solar cell module.

  Solar power generation is being put into practical use as an inexhaustible and non-polluting new energy source, and as a solar cell module for this purpose, a surface protection sheet, an adhesive resin layer, a solar cell, an adhesive resin layer, and a back surface protection sheet are used. Laminated and integrated products are widely known.

  Although the back surface protection sheet is not directly exposed to sunlight, depending on the installation method, the back surface protection sheet is exposed to sunlight due to wraparound or reflection. Therefore, it is important to impart ultraviolet resistance (UV) resistance to the back surface protection sheet.

  As a back surface protection sheet conventionally used, a white polyvinyl fluoride film (DuPont Co., Ltd. “Tedlar” (registered trademark)) can be exemplified, and a back surface protection sheet having a laminated structure in which a polyester film is sandwiched between the films is Widely used in such applications. The polyvinyl fluoride film is excellent in UV resistance, but is expensive and becomes an obstacle in terms of reducing the cost of the solar cell module. Moreover, since it contains fluorine, it has a problem of high disposal costs.

  In recent years, a back surface protective sheet in which an ultraviolet protective layer is laminated on a base film such as polyester has been proposed. Since the ultraviolet protective layer blocks the intrusion of light from the back surface, the base material is versatile and the cost can be reduced (Patent Document 1).

  By the way, in the case of a configuration in which an ultraviolet protective layer is provided, durability of the ultraviolet protective layer itself and long-term durability of the base film are important. Recently, long-term quality assurance of 20 to 30 years after installation has been demanded, and the demand for long-term durability has been increasing year by year. For this purpose, the ultraviolet protective layer must be firmly maintained on the base film even by contact with wind and sand, and the scratch resistance of the ultraviolet protective layer needs to be further improved.

International Publication No. 2010/067780

  The problem to be solved by the present invention is to provide a back protective sheet for a solar cell module, which is excellent in scratch resistance of an ultraviolet protective layer and has good long-term durability.

  In order to solve the above problems, the present invention has the following configuration.

  1st invention is a back surface protection sheet for solar cell modules which consists of a polyester film and an ultraviolet protective layer at least, Comprising: This ultraviolet protective layer contains a resin component and an inorganic particle, The light transmission in wavelength 360nm of this ultraviolet protective layer The back protective sheet for solar cell module, characterized in that the rate is 5% or less and the center plane average roughness of the ultraviolet protective layer is 0.05 μm or more and 0.12 μm or less.

  The second invention is characterized in that the proportion of the inorganic particles in the ultraviolet protective layer is 5% by volume or more and 20% by volume or less.

  According to a third aspect of the present invention, the thickness in terms of inorganic particles expressed by the product of the thickness (μm) of the ultraviolet protective layer and the ratio (volume%) of inorganic particles in the ultraviolet protective layer is 0.15 μm or more. It is characterized by being 5 μm or less.

  In a fourth aspect of the invention, the average primary particle diameter of the inorganic particles is 0.1 μm or more and 1.0 μm or less, and the thickness of the ultraviolet protective layer is 4 times or more and 40 times or less of the average primary particle diameter of the inorganic particles. It is characterized by that.

  ADVANTAGE OF THE INVENTION According to this invention, the back surface protection sheet for solar cell modules which is excellent in the abrasion resistance of an ultraviolet-ray protective layer and can endure long-term use can be provided.

  The present invention will be described below.

  The back surface protection sheet for solar cell modules of this invention consists of a polyester film and an ultraviolet protection layer at least.

[Polyester film]
Since the polyester film used in the present invention is used in the outermost layer that is directly exposed to the outside air, the polyester film is preferably a polyester film having excellent hydrolysis resistance. In general, a polyester film contains 1.5 to 2% by weight of a low molecular weight polymer called an oligomer. Typical examples of polyester oligomers are cyclic trimers, and films containing a large amount of them have reduced mechanical strength during long-term exposure, such as outdoors, and cracks and material breaks associated with the progress of hydrolysis due to rainwater, etc. Produce. On the other hand, by forming a polyester film from a polyester having a cyclic trimer content of 1.0% by weight or less obtained by polymerization by a solid phase polymerization method, hydrolysis under high temperature and high humidity In addition, a film excellent in heat resistance and weather resistance can be obtained. The content of the cyclic trimer is obtained, for example, by a method of measuring the content (% by weight) relative to the resin weight by measuring by liquid chromatography using a solution obtained by dissolving 100 mg of a polymer in 2 ml of orthochlorophenol. It is done.

  In addition, the polyester film may be added with additives such as an antistatic agent, an ultraviolet absorber, a stabilizer, an antioxidant, a plasticizer, a lubricant, a filler, and a coloring pigment, if necessary. A polyester film or the like added within a range that is not impaired can also be used.

  The thickness of the polyester film is not particularly limited, but is preferably in the range of 25 to 300 μm in view of the withstand voltage characteristics and cost of the back protective sheet.

[UV protective layer]
The ultraviolet protective layer in the present invention is selected in consideration of weather resistance, heat resistance, UV resistance, adhesion to a base polyester film, etc., in addition to the ultraviolet absorptivity for performing the original function, and the resin component and Contains inorganic particles. The UV protection layer is a layer disposed on the outermost layer of the back surface protection sheet, and protects the back surface protection sheet laminated on the back surface side of the solar cell module from ultraviolet irradiation from the back surface side of the module. It has a function and is applied onto the polyester film and introduced into the back surface protective sheet.

  In order to develop durability over a long period of 20 to 30 years after installation, it is necessary to make the light transmittance at 360 nm of the ultraviolet protective layer 5% or less and to suppress deterioration with time of the polyester film due to ultraviolet rays.

  For this purpose, the ultraviolet protective layer needs to be maintained for a long period of time, and the scratch resistance of the ultraviolet protective layer is important. When the surface of the ultraviolet protective layer is rough, for example, sand and pebbles collide and are rubbed off, so that the ultraviolet protective layer is easily scraped off. In order to obtain an ultraviolet protective layer having excellent scratch resistance, it is important that the average surface roughness of the ultraviolet protective layer is 0.12 μm or less. On the other hand, the average surface roughness of the UV protective layer needs to be 0.05 μm or more. If the average surface roughness of the UV protective layer is less than 0.05 μm, the UV protective layer becomes glossy. , Gloss unevenness may occur, resulting in poor design.

  In addition to the structure for achieving the above functions, the ultraviolet protective layer may be added with a coloring agent according to the purpose in order to impart design properties.

  The ultraviolet protective layer contains, as main components, inorganic particles that are colorants that absorb or reflect ultraviolet rays, and a resin as a binder for fixing the particles. The resin preferably has a cross-linked structure from the viewpoint of long-term weather resistance, and relatively inexpensive acrylic resins, urethane resins, styrene resins, and the like are preferably used. It is preferable to form a crosslinked structure by reacting a composition comprising a polyol-based binder resin having a hydroxyl group serving as a crosslinking base in the polymer structure and a polyisocyanate crosslinking agent in the coating process.

  As the resin component used in the UV protective layer, acrylic resins and polyurethane resins having excellent weather resistance can be used. As the acrylic resins, acrylic resins, acrylic polyol copolymers, acrylic / urethane copolymers can be used. Etc. are used. For example, “Acrynal” (registered trademark) (manufactured by Toei Kasei Co., Ltd.), “Acryt” (manufactured by Taisei Fine Chemical Co., Ltd.), “Hitaroid” (registered trademark) (manufactured by Hitachi Chemical Co., Ltd.), “Acridick” (Registered trademark) (manufactured by DIC Corporation), “Udable” (registered trademark) (manufactured by Nippon Shokubai Co., Ltd.), “Dianar” (registered trademark) (Mitsubishi Rayon Co., Ltd.), and the like. Examples of the polyurethane resin include “Samprene” (registered trademark) (manufactured by Sanyo Chemical Industries), “Takelac” (registered trademark) (manufactured by Mitsui Chemicals), “TA” (Hitachi Chemical Polymer Co., Ltd.). And Seika Bond (registered trademark) (manufactured by Dainichi Seika Kogyo Co., Ltd.). These resins are desirably used in a mixture of two or more resins in the same resin system.

  The inorganic particles used in the ultraviolet protective layer are preferably used for a long time outdoors, and therefore, an inorganic pigment with high light stability is preferable. From the viewpoint of availability, price, and light reflectivity, titanium oxide is preferable. Preferably used. The average primary particle size of titanium oxide is preferably 0.1 to 1.0 μm from the viewpoint of color development, dispersibility with respect to the binder resin and cost, and more preferably from 0.15 μm to 0.5 μm from the viewpoint of scratch resistance of the ultraviolet protective layer. Or less, more preferably 0.15 μm or more and 0.3 μm or less. Particularly, titanium oxides for pigments having an average primary particle size of 0.15 μm or more and 0.5 μm or less are manufactured industrially at low cost and can be easily used. If the average primary particle size of the inorganic particles is less than 0.1 μm, the manufacturing cost increases. On the other hand, if the average primary particle size of the inorganic particles exceeds 1.0 μm, the unevenness of the surface of the ultraviolet protective layer becomes large, and the scratch resistance decreases, which is not preferable.

  In the ultraviolet protective layer of the present invention, the proportion of inorganic particles in the ultraviolet protective layer is preferably 5% by volume or more and 20% by volume or less. When the proportion of the inorganic particles is less than 5% by volume, the ultraviolet reflection performance is insufficient, and the base polyester film may not be sufficiently protected from ultraviolet rays. On the other hand, if the volume exceeds 20% by volume, the surface of the ultraviolet protective layer becomes rough, so that when the surface of the ultraviolet protective layer is rubbed, the ultraviolet protective layer is easily peeled off from the polyester film, and the scratch resistance tends to be reduced. It is in.

  In the ultraviolet protective layer in the present invention, a curing agent having a functional group capable of reacting with a hydroxyl group in the acrylic resin is preferably blended for the purpose of improving the properties of the resin layer. By blending the curing agent, the effects of improving the adhesion between the polyester film and the ultraviolet protective layer and improving the durability of the ultraviolet protective layer accompanying the introduction of the crosslinked structure can be obtained. In particular, when designing the back surface protection sheet for solar cell modules so that the ultraviolet protection layer is located in the outermost layer, in the manufacturing process of the solar cell module, specifically in the glass laminating step (cell filling step), Since the ultraviolet protective layer is exposed to a heat treatment of 30 minutes or longer at a high temperature of about 150 ° C. at the maximum, particularly heat resistance is required, and it is preferable to use a crosslinking agent that can react with the hydroxyl group of the binder resin. Among them, a prescription that uses a polyisocyanate curing agent and promotes the formation of urethane bonds (crosslinked structure) is preferable. Examples of the polyisocyanate-based crosslinking agent used as the crosslinking agent include aromatic polyisocyanates, araliphatic polyisocyanates, alicyclic polyisocyanates, and aliphatic polyisocyanates.

  Examples of the solvent for the coating liquid for forming the ultraviolet protective layer in the present invention by a coating method include toluene, xylene, ethyl acetate, propyl acetate, butyl acetate, acetone, methyl ethyl ketone, methyl isobutyl ketone, methanol, ethanol, water, and the like. Can be illustrated. The properties of the coating liquid may be either an emulsion type or a dissolution type.

  The method for forming the ultraviolet protective layer on the substrate film is not particularly limited, and a known coating technique can be used. As the coating method, various methods can be applied. For example, a roll coating method, a dip coating method, a bar coating method, a die coating method, a gravure roll coating method, or a combination of these methods can be used. it can.

  The thickness of the ultraviolet protective layer in the present invention is preferably 1 to 10 μm, more preferably 1.5 to 8 μm, and particularly preferably 2 to 5 μm. When this ultraviolet protective layer is formed by a coating method, if the thickness is less than 1 μm, a phenomenon such as repellency or film breakage tends to occur during coating, and it is difficult to form a uniform coating film. Adhesive strength, UV-cutting properties, peeling resistance, and scratch resistance may not be sufficiently exhibited. On the other hand, when the thickness of the UV protective layer exceeds 10 μm, UV blocking performance is fully expressed, but there are restrictions on the coating method (specific processes that can be applied to thick films, restrictions on equipment), and the production cost increases. There is a concern that the coating film sticks to the transport roll and the coating film peels off easily.

  In the present invention, when the product of the thickness of the ultraviolet protective layer and the ratio of the inorganic particles in the ultraviolet protective layer is defined as “inorganic particle equivalent thickness”, the inorganic particle equivalent thickness is 0.15 μm or more and 1.5 μm or less. More preferably, it is 0.2 μm or more and 1.5 μm or less, and further preferably 0.3 μm or more and 1.5 μm or less. When the inorganic particle equivalent thickness is less than 0.15 μm, ultraviolet rays reaching the polyester film cannot be sufficiently blocked, and the polyester film deteriorates with time due to the ultraviolet rays, causing problems such as generation of cracks. Sometimes. Further, if the thickness in terms of inorganic particles exceeds 1.5 μm, it is necessary to increase the thickness of the ultraviolet protective layer or increase the proportion of inorganic particles in the ultraviolet protective layer, which may increase the cost. .

  Furthermore, the thickness of the ultraviolet protective layer in the present invention is preferably 4 to 40 times the average primary particle diameter of the inorganic particles. If the thickness of the ultraviolet protective layer is less than 4 times the average primary particle diameter of the inorganic particles, the ultraviolet blocking performance of the ultraviolet protective layer is lowered, and the base polyester film may be deteriorated in long-term outdoor use. On the other hand, when the thickness of the ultraviolet protective layer exceeds 40 times the average primary particle diameter of the inorganic particles, the ultraviolet protective layer becomes thicker than necessary, which may increase costs.

  In the ultraviolet protective layer of the present invention, a plasticizer, a heat stabilizer, an antioxidant, a reinforcing agent, a deterioration preventing agent, a weathering agent, a flame retardant, a release agent, etc. may be added as long as the characteristics are not impaired. Good.

[Back protection sheet]
In the present invention, if necessary, a white film, a film having a metal oxide vapor-deposited layer on the surface opposite to the ultraviolet protective layer of the film, and an ethylene / vinyl acetate copolymer resin (EVA) which is a sealing material for a solar cell element; By laminating one or more kinds of films different from the base film among the films having thermal adhesive properties, a back protective sheet for a solar cell module that satisfies various required characteristics can be obtained.

  As the white film, “Lumirror” (registered trademark) E20F manufactured by Toray, which is a polyethylene terephthalate film, “Tedlar” (registered trademark) PV2001, manufactured by DuPont, which is a polyvinyl fluoride film, and “Kiner” manufactured by Arkema, which is a polyvinylidene fluoride film. "(Registered trademark) 302-PGM-TR" can be exemplified. An example of a film having an inorganic oxide vapor deposition layer is “Barrier Rocks” (registered trademark) 1011HG manufactured by Toray Film Processing Co., Ltd., in which a metal oxide vapor deposition layer made of aluminum oxide is formed on a polyethylene terephthalate film substrate. it can. Examples of the film having thermal adhesiveness with EVA include polyolefin films such as ZK93K, 4801, 4806, and B011W manufactured by Toray Film Processing Co., Ltd. When a white film is laminated, light reflectivity is imparted, when a film having a metal oxide vapor deposition layer is laminated, water vapor barrier property is imparted, and when an olefin film layer is laminated on the side facing the EVA Becomes excellent in thermal adhesiveness with EVA. Moreover, the film laminated | stacked on the back surface protection sheet for solar cell modules in this invention does not necessarily need to be 1 sheet, According to the characteristic to provide, each member film is combined suitably and the back surface protection sheet for solar cell modules should be designed. It ’s fine.

  In addition, in the configuration of the back surface protection sheet for solar cell modules, a vapor deposition layer, a sputter layer, a wet coating layer, or the like for the purpose of imparting functionality is formed on any layer as long as it is not on the ultraviolet protective layer. May be.

  A known dry laminating method can be used as a method of laminating films and processing into sheets. Bonding of the resin film using the dry laminating method includes a main component such as a polyether polyurethane resin, a polyester polyurethane resin, a polyester resin, a polyepoxy resin, and a polyisocyanate curing agent. A known dry laminating adhesive can be used. However, the adhesive layer formed using these adhesives does not cause peeling due to deterioration of the adhesive strength due to long-term outdoor use, which leads to deterioration in appearance and light reflectance. It is necessary not to cause yellowing. Moreover, as thickness of an adhesive bond layer, Preferably it is the range of 1-5 micrometers. If it is less than 1 μm, it may be difficult to obtain sufficient adhesive strength. On the other hand, if it exceeds 5 μm, the coating speed of the adhesive does not increase, and the amount of the adhesive used increases, leading to an increase in production cost.

  As a material for the adhesive layer, a known dry laminating adhesive can be used. In general, adhesives for dry laminating are prepared by diluting two components of the main agent and cross-linking agent with a diluting solvent. The cross-linking agent is highly reactive with active hydroxyl groups, its reaction rate and initial adhesion. A prescription using an isocyanate group-containing oligomer with a fast onset is preferred. In addition to these advantages, it is possible to form an adhesive resin layer that has high adhesive strength with the base film, and also has excellent constant temperature stability and long-term durability. Examples of the main resin used in combination with the isocyanate group-containing oligomer include polyether resins, polyester resins, polyol resins, and other urethane resins and epoxy resins, depending on detailed requirements and suitability for processing conditions. Can be appropriately selected and used. Moreover, depending on the structure of the back surface protection sheet for solar cell modules, it is also conceivable that UV light reaches the adhesive layer and induces photodegradation of the resin. From such a viewpoint, the resin used for forming the adhesive layer is preferably an aliphatic resin or an alicyclic resin that does not contain an aromatic ring or has a low content.

  Hereinafter, the present invention will be described with reference to examples.

  The characteristic values in the examples and comparative examples of the present invention are based on the following measurement methods and evaluation criteria.

[Thickness of UV protection layer]
The coating amount W (g / m ² ) of the ultraviolet protective layer was measured by the following method. After forming the ultraviolet protective layer, it was cut into an area of 500 cm ² , and the mass of the test piece was weighed with an effective number of 1 mg using an electronic balance ELECTRONIC BALANCE UW420H manufactured by Shimadzu Corporation to obtain a mass W1. Next, the resin layer was dissolved in methyl ethyl ketone from the test piece, peeled off, blown with a dryer to evaporate and remove the methyl ethyl ketone, and then the mass of the test piece was measured again to obtain mass W2. Subsequently, the coating amount per unit area was calculated based on the following formula (1). This coating amount measurement was performed on three test pieces, and the average value was taken as the coating amount.

Application amount W (g / m ² ) = (W1−W2) × 20 (1)
Further, the density D (g / cm ³ ) of the ultraviolet protective layer was measured by the following method. As the density measurement sample, the ultraviolet protective layer was scraped off from the film on which the ultraviolet protective layer was formed with a ceramic spatula to obtain about 0.05 g of the powder of the ultraviolet protective layer. The density was measured using an Ultrapycnometer 1000 model manufactured by QUANTACHROME INSTRUMENTS in accordance with the gas displacement method of JIS K7112 (1999). A nanocell with a volume of 0.25 cc was used, and helium was used as the gas used.

From the coating amount W (g / m ² ) of the ultraviolet protective layer obtained above and the density D (g / cm ³ ) of the ultraviolet protective layer, the thickness A (μm) of the ultraviolet protective layer is expressed by the following formula (2 ).

A (μm) = W / D (2)
[Average surface roughness (SRa) of UV protective layer]
Using a fully automatic fine shape measuring machine (SURFCORDER ET4000A) manufactured by Kosaka Laboratory Co., Ltd., in accordance with JIS B0601 (1982), the measurement length is 4 mm in the lateral direction and the pitch is 10 μm in the longitudinal direction (machine direction). Was measured 10 times and analyzed three-dimensionally to obtain the center plane average roughness (SRa) (unit: μm). Note that a diamond needle having a tip radius of 2.0 μm and a vertex angle of 60 ° was used, and measurement was performed at a measuring force of 100 μN and a cutoff of 0.8 mm.

[Average primary particle size of inorganic particles]
The average primary particle diameter of the inorganic particles is a particle diameter of primary particles defined as particles generated by growth of a single crystal nucleus in JIS H7008 (2002). The particle diameter of the primary particles (hereinafter referred to as the primary particle diameter) is an average value of the major axis and the minor axis. For the measurement of such primary particle diameter, according to JIS H7804 (2005), using a scanning electron microscope (SEM), the sample is observed at a magnification of 10,000 times, and a photograph is used to measure the long diameter and short diameter of each primary particle. The diameter is measured, the primary particle diameter is obtained by the average, and the primary particle diameter is similarly measured for 20 primary particles, and the average value is taken as the average primary particle diameter.

[Light transmittance of UV protective layer]
In order to measure the light transmittance of the ultraviolet protective layer at a wavelength of 360 nm, it was measured using a 5 cm square test piece using MPC3100-PC manufactured by Shimadzu Corporation. Since polyester film absorbs light of 360 nm wavelength, UV protection is applied to ETFE film using ETFE film “Toyoflon” (registered trademark) 50E manufactured by Toray Film Processing Co., Ltd. with a thickness of 50 μm, which absorbs light of 360 nm wavelength little. The layer was applied to prepare a measurement sample. Then, the light transmittance at 360 nm of the coating layer was determined by the ratio of the transmittance of the 50 μm ETFE film “Toyoflon” 50E to the light transmittance at 360 nm of the film coated with the ultraviolet protective layer. It was judged that the light transmittance at 360 nm was less than 5% as a practical range.

[Abrasion resistance of UV protective layer]
In order to evaluate the scratch resistance of the ultraviolet protective layer, a test was conducted under the following conditions. A measurement sample with a UV protective layer provided on a base polyester film is prepared, and the UV protective layer is set on a Gakushin-type wear tester (Friction Tester Type II of JIS L0849) on the upper surface. Using "No. 3", 20 reciprocating frictions are performed with a load of 200 g. The state of the ultraviolet protective layer surface after the test was determined according to the following evaluation criteria. ○ and △ were accepted, and x was rejected.

  ○: No more than 5 scratches on the scratched surface.

  Δ: 6-20 scratches on the scratched surface.

  X: 21 or more scratches were generated on the scratched surface.

[Adhesion of UV protective layer]
Regarding the adhesion of the UV protective layer to the base polyester film, in accordance with ISO 2409 (2013), the UV protective layer is cut on a lattice, and a tape is applied thereto at an angle of 60 °, 0.5 seconds to 1 second. Peel off at the peeling time and check the peeling state.

  The ultraviolet protective layer in the present invention is required to have class 0 adhesion of the substrate. Classes are classified as follows. If it is Class 1 or higher, adhesion during production and use cannot be guaranteed.

  Class 0: The edges of the cut are completely smooth and there is no peeling on the eyes of any lattice.

  Class 1: Small peeling of the coating film at the intersection of cuts (degree of peeling: 5% or less).

  Class 2: The coating film is peeled along the edge of the cut and / or at the intersection (degree of peeling: 5% to 15%).

  Class 3: The paint film is partially or completely peeled along the edge of the cut, or various parts of the eye are partially or completely peeled off (degree of peeling: 15% ~ 35%).

  Class 4: The coating film is partially or completely peeled along the edge of the cut, or some eyes are partially peeled completely (degree of peeling: 35% to 65 %).

  Class 5: Large peeling that cannot be classified into any of classes 0 to 4 occurs.

[Retention rate at break after UV irradiation]
Using Iwasaki Electric Co., Ltd. Eye Super UV Tester SUV-W151 which is an accelerated weathering tester, using an illuminometer, the UV intensity is adjusted to 1000 W / m ² in an atmosphere of 63 ° C. and 30% relative humidity. To do. Under the conditions of the present apparatus, the back surface protective sheet for solar cell module of the present invention was irradiated with ultraviolet rays for 316 hours on the ultraviolet protective layer side.

  Using the test method described in JIS C2151 (1996), using a test piece having a width of 10 mm and a length of 150 mm, the initial distance between the chucks was 55 mm, and the breaking elongation of the back protective sheet was set at a pulling speed of 300 mm / min. It was measured. The value of (B) / (A) × 100 (%) was determined as the breaking elongation retention rate from the breaking elongation (B) after ultraviolet irradiation with respect to the breaking elongation (A) before ultraviolet irradiation. The evaluation was performed with 5 samples each in the longitudinal direction of the back protective sheet, and the average value of these 5 samples was represented.

  A practical range of 50% or higher fracture elongation retention after UV irradiation was determined.

Preparation of the coating material for forming an ultraviolet protective layer in the present invention is as follows.
The composition according to Table 1 was dispersed using a paint shaker (using glass beads with a diameter of 2 mm) to prepare a paint for forming an ultraviolet protective layer.

[How to find the proportion (volume%) of inorganic particles in the UV protective layer]
The weight of the inorganic particles to be blended in the UV protective layer-forming coating material is X (g), the density is D1 (g / cm ³ ), and the solid content weight of the resin (solid content weight of the main agent + solid content weight of the curing agent) is Y (g), the density is D2 (g / cm ³ ), the volume of inorganic particles in the ultraviolet protective layer is V1 (cm ³ ), and the volume of the resin component in the ultraviolet protective layer is V2 (cm ³ ). The proportion (volume%) B of inorganic particles in the protective layer was calculated by the following formulas (3) to (5).

V1 (cm ³ ) = X / D1 (3)
V2 (cm ³ ) = Y / D2 (4)
B (%) = V1 ÷ (V1 + V2) × 100 (5)
[Adjustment of adhesive for dry lamination]
12 parts by weight of dry laminating agent “Takelac” (registered trademark) A-310 (polyester polyurethane resin) manufactured by Mitsui Chemicals Polyurethane Co., Ltd. “Takenate” which is an aromatic polyisocyanate compound manufactured by Mitsui Chemicals Polyurethanes (Registered Trademark) 1 part by weight of A-3 and 212 parts by weight of ethyl acetate were weighed and stirred for 15 minutes to obtain an adhesive for dry lamination having a solid content concentration of 3% by weight.

[Example 1]
As a polyester film, a hydrolysis-resistant polyethylene terephthalate film “Lumirror” (registered trademark) X10S (125 μm) manufactured by Toray Industries, Inc. was prepared. One side of this polyester film is subjected to corona treatment, and a coating A is applied using a wire bar and dried at 150 ° C. for 30 seconds. After drying, the coating amount is 8 g / m ² (the solid content specific gravity of the UV protective layer). An ultraviolet protective layer is provided so that the coating thickness converted to 1.73 g / cm ³ is 4.6 μm), and aging is performed at a temperature of 40 ° C. for 72 hours to accelerate the curing reaction of the ultraviolet protective layer, and the solar cell module A coated film for use in a backside protective sheet was obtained.

Furthermore, a dry laminating adhesive was applied to the opposite side of the UV protective layer of the coated film using a wire bar and dried at 150 ° C. for 30 seconds. After drying, the coating amount was 5 g / m ^2. Lamination with a white polypropylene film B011W (150 μm) manufactured by Film Processing Co., Ltd. was performed. The laminated film was aged at a temperature of 40 ° C. for 72 hours to promote the curing reaction of the adhesive layer, thereby obtaining a back surface protection sheet for a solar cell module.

  The evaluation results of the obtained back surface protective sheet for solar cell module are shown in Table 2. The scratch resistance of the ultraviolet protective layer was good.

[Example 2]
A solar cell was produced in the same manner as in Example 1 except that the coating amount after drying of the coating material A was 2 g / m ² (the coating thickness converted to a solid specific gravity of 1.73 g / cm ³ of the ultraviolet protective layer was 1.2 μm). A back protective sheet for modules was obtained. Since the thickness of the ultraviolet protective layer was thin, the UV resistance was inferior, but it was at a level causing no practical problems.

[Example 3]
Example 1 except that paint B was used in place of paint A, and the coating amount after drying was 13 g / m ² (the coating thickness converted to a solid content specific gravity of 1.73 g / cm ³ of the UV protective layer was 7.5 μm). The back surface protection sheet for solar cell modules was obtained by the same method. Although the primary particle diameter of titanium oxide blended in the UV protective layer was large and the average roughness of the center plane of the UV protective layer was increased, the scratch resistance was at a level that was not a problem for practical use.

[Example 4]
Example 1 except that paint C was used in place of paint A, and the coating amount after drying was 13 g / m ² (the coating thickness converted to a solid content specific gravity of 1.34 g / cm ³ of the UV protective layer was 9.7 μm). The back surface protection sheet for solar cell modules was obtained by the same method. By reducing the proportion of the inorganic particles in the ultraviolet protective layer, the average roughness of the central surface of the ultraviolet protective layer can be reduced, and the scratch resistance was very good.

[Comparative Example 1]
Example 1 except that paint C was used instead of paint A, and the coating amount after drying was 3 g / m ² (the coating thickness converted to a solid content specific gravity of 1.34 g / cm ³ of the UV protective layer was 2.2 μm). The back surface protection sheet for solar cell modules was obtained by the same method. Since the proportion of inorganic particles in the ultraviolet protective layer was small and the coating thickness was thin, the equivalent inorganic particle thickness was thin, resulting in poor UV resistance and poor adhesion.

[Comparative Example 2]
Example 1 except that paint D was used in place of paint A, and the coating amount after drying was 10 g / m ² (the coating thickness converted to a solid content specific gravity of 1.91 g / cm ³ of the UV protective layer was 5.2 μm). The back surface protection sheet for solar cell modules was obtained by the same method. Since the proportion of inorganic particles in the ultraviolet protective layer was large, the average roughness of the central surface of the ultraviolet protective layer was increased, resulting in poor scratch resistance.

As is clear from the results of the above examples and comparative examples, according to the method of the present invention, a solar cell module having an ultraviolet protective layer excellent in scratch resistance and excellent in long-term durability when used in the outermost layer. It can be used as a backside protection sheet.

Claims (4)

  A back protective sheet for a solar cell module comprising at least a polyester film and an ultraviolet protective layer, wherein the ultraviolet protective layer contains a resin component and inorganic particles, and the ultraviolet protective layer has a light transmittance of 5% or less at a wavelength of 360 nm. A back surface protective sheet for a solar cell module, wherein the ultraviolet protective layer has a center surface average roughness of 0.05 μm or more and 0.12 μm or less.   The back surface protective sheet for a solar cell module according to claim 1, wherein the proportion of the inorganic particles in the ultraviolet protective layer is 5% by volume or more and 20% by volume or less.   The inorganic particle equivalent thickness represented by the product of the thickness (μm) of the ultraviolet protective layer and the proportion (volume%) of the inorganic particles in the ultraviolet protective layer is 0.15 μm or more and 1.5 μm or less. The back surface protection sheet for solar cell modules of Claim 1 or 2 characterized by these. The average primary particle diameter of the inorganic particles is 0.1 μm or more and 1.0 μm or less, and the thickness of the ultraviolet protective layer is 4 to 40 times the average primary particle diameter of the inorganic particles. Item 4. A back protective sheet for a solar cell module according to any one of Items 1 to 3.