JP2012204772A - Solar battery module and rear surface protective sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To impart high reflectance characteristics to a dark color, such as black, rear surface protective sheet for a solar battery.SOLUTION: A solar battery module 1 includes a solar battery cell 10 converting the sunlight to electrical energy. In the solar battery module 1, a rear surface protective sheet 25 for reflecting the sunlight incident from the surroundings of the solar battery cell 10 is arranged on a side of the solar battery cell 10, the side being opposite to a light receiving surface. The rear surface protective sheet 25 has an irregular-shaped layer including a metal reflection layer, and the irregular-shaped layer is formed such that a plurality of projecting parts or recessed parts have a period of 190 nm or longer and 600 nm or shorter.

Description

  The present invention relates to a solar cell module and a back surface protection sheet used therefor.

In recent years, solar cells have been attracting attention as a clean energy source due to increasing awareness of environmental problems, and solar cell modules having various forms are currently being developed and used in various fields (see Patent Document 1).
This solar cell converts incident light energy into electric energy, and the main ones of the solar cells are classified into crystalline silicon type, amorphous silicon type, organic compound type, etc. depending on the type of material used. Among these, most of those currently on the market are crystalline silicon solar cells, which are further classified into single crystal type and polycrystalline type.

Single-crystal silicon solar cells have the advantage that the substrate quality is good and the efficiency can be easily increased, but the substrate is expensive to manufacture. In contrast, polycrystalline silicon solar cells have the disadvantage of being difficult to achieve high efficiency due to poor substrate quality, but have the advantage that they can be manufactured at low cost, and are currently the mainstream.
Using the solar cell element as described above, a surface sheet layer, a filler layer, a solar cell element as a photovoltaic element, a filler layer, a back surface protection sheet layer, etc. Manufactured by using a lamination method in which suction is applied and thermocompression bonding is performed.

  As the back surface protection sheet layer constituting the solar cell module, a plastic base material having excellent strength is most commonly used at present, and a metal plate or the like is also used. Thus, in general, as the back surface protection sheet layer constituting the solar cell module, for example, it has excellent strength, weather resistance, heat resistance, water resistance, light resistance, chemical resistance, and light reflectivity. , Excellent in light diffusivity, etc., in particular, excellent in moisture resistance to prevent intrusion of moisture, oxygen, etc., and also has high surface hardness and excellent antifouling property to prevent accumulation of dirt, dust, etc. on the surface, It is required to satisfy the conditions such as extremely high durability, high protection ability, and other factors.

  Moreover, the back surface provided in the back surface side of the said photovoltaic cell, without injecting into the photovoltaic cell which converts energy within a photovoltaic module among the sunlight which injected from the front surface of the photovoltaic module in order to improve light utilization efficiency Attempts have been made to reuse sunlight incident on the protective sheet (see Patent Document 2).

  As the back surface protective sheet layer constituting the solar cell module, a laminate of white thermoplastic resin sheets that scatter light is known in order to increase the reflectance of sunlight and increase the energy conversion of the solar cell. (See Patent Documents 3 and 4). Attempts have also been made to make the surface of the reflector have an uneven structure. By making the surface of the reflective material an uneven structure, it is possible to further improve the light utilization efficiency (see Patent Document 5).

However, for example, a metal such as aluminum is used as the reflective material of the concavo-convex structure, but aluminum is easily corroded by moisture, acid, etc. and cannot withstand the natural environment for more than 10 years, and the effect of improving the light utilization efficiency Is a problem. In addition, when arranging solar cells on the roof of a house, it is preferred to be colored in a dark color such as black, from the viewpoint of appearance considering the balance with the whole house, There is a need for a back sheet for a solar cell colored in the above color.
However, the back surface protection sheet colored in a dark color is generally a sheet made of carbon black, carbon black absorbs sunlight, the temperature rises, there is a possibility that the power generation efficiency is reduced, It is not preferable.

JP 2001-295437 A JP 2000-332279 A JP 2006-270025 A JP 2007-177136 A Japanese Patent Application Laid-Open No. 11-307791

  The present invention is a back surface protection sheet that has a dark color appearance such as black and is excellent in terms of appearance, and can improve light utilization efficiency as compared with a back surface protection sheet having a conventional dark color appearance. A back surface protection sheet that minimizes long-term performance degradation, prevents acid and the like generated by hydrolysis and fillers, and is extremely durable and constitutes a solar cell module at a lower cost. It is to provide a solar cell module using a stable.

In order to solve the above-described problems, the present invention proposes the following means.
In the solar cell module provided with solar cells that convert into electric energy, the back surface that reflects sunlight incident from the periphery of the solar cells to the solar cell side on the side opposite to the light receiving surface of the solar cells. A protective sheet is disposed, and the back surface protective sheet includes a concavo-convex shape layer provided with a metal reflection layer, and the concavo-convex shape layer is formed with a period of a plurality of convex portions or concave portions being 190 nm or more and 600 nm or less. Yes.

Here, the period refers to a distance obtained by measuring two corresponding points of adjacent convex portions or concave portions in parallel with the direction in which the protective sheet extends, and is a word corresponding to a pitch in terms of threads.
Light that is incident on the back surface protection sheet without being received by the light receiving surface is returned to the incident surface side by diffracted light due to the concavo-convex shape, and is totally reflected by the front plate provided in the solar cell module. The power generation efficiency can be improved by entering the cell.

When a plurality of convex portions or concave portions are arranged with a minute cycle as described above, regular reflection is reduced, and the entire back surface protection sheet can be visually recognized around the solar battery cell, so that the whole looks dark. Appearance is improved.
The concave-convex layer is preferably arranged so that the period of the plurality of convex portions or concave portions is 200 nm or more and 400 nm or less.

Within the above-mentioned range, specular reflection is further reduced, and almost no diffracted light is generated even in a state where the back surface protection sheet can be directly visually recognized around the solar battery cell, and the appearance looks better because the whole looks more blackish. .
In the concavo-convex shape layer, the depth or height of the convex portion or the concave portion may be ½ times or more and less than 1 time of their period.

  The concavo-convex structure layer becomes darker when the depth or height of the convex portion or the concave portion is increased, and the depth or height of the concave portion or the convex portion is ½ times or more the distance between the centers thereof. If there is, it will look very dark. Further, the deeper the concave or convex, the darker the higher the higher the concave or convex part, but the reflectivity of the concavo-convex shape layer provided with the metal reflective layer decreases, and the light to be reused is preferably reduced. Absent. If the depth or height of the concave portion or the convex portion is less than 1 time between the centers, the reduction of light to be reused is small.

A weather resistant layer, a metal reflective layer, a concavo-convex shape layer, and a light-transmissive insulating layer are sequentially provided from the rearmost surface side to the front surface side of the back surface protection sheet, and between the weather resistant layer and the metal reflective layer and / or metal reflective layer. It is preferable to provide at least one barrier layer between the layer and the concavo-convex shape layer.
By laminating the barrier layer, intrusion of moisture, acid and the like can be prevented, and corrosion of the metal reflective layer can be prevented and long-term stability can be improved.

The metal reflective layer may have a thickness of 5 nm to 100 nm.
The general metal layer of the metal reflection layer has a reflectivity that depends on the film thickness, and is preferably 40 nm or more. If the thickness is approximately 40 nm or more, the reflectivity is stable at a high reflectivity. On the other hand, when the thickness is smaller than 40 nm, a decrease in reflectance clearly appears. In order to exhibit an effect as a metal layer that can be visually recognized, a thickness of 5 nm or more is required. On the other hand, if the thickness is 100 nm or more, cracks that can be visually recognized occur.

The weather-resistant layer and the light-transmitting insulating layer are made of a thermoplastic resin, and the glass transition temperature of these thermoplastic resins is preferably lower than the glass transition temperature of the resin constituting the concavo-convex shape layer. .
If it is the above structures, even if it is bent, the occurrence of cracks and the like is suppressed, the balance between heat resistance and flexibility is improved, and the dimensional change rate is small.

The thickness of the transparent insulating layer is preferably 50 μm or more and 500 μm or less.
Within the above-mentioned range, the back surface protective sheet is excellent in flexibility. If it is 50 μm or less, it has a partial discharge, and if it is 500 μm or more, cracking occurs when it is bent, resulting in poor flexibility.
Furthermore, according to the said back surface protection sheet, the solar cell module which has said each effect can be formed.

  The solar cell module according to the present invention is excellent in heat resistance, flexibility, and weather resistance. And the regular reflection is reduced by the concavo-convex shape layer, and the entire back surface has a dark color appearance such as black even in a state where the back surface protection sheet can be directly visually recognized around the solar battery cell, and the power generation efficiency can be improved. . Moreover, according to the back surface protection sheet of this invention, the solar cell module with the said effect can be formed.

It is sectional drawing which shows schematic structure of the solar cell module of embodiment. It is an expanded sectional view of the back surface protection sheet of FIG. It is sectional drawing which shows schematic structure of another form of a back surface protection sheet. It is a perspective view which shows an example of the uneven | corrugated shape employable as an uneven | corrugated structure area | region. It is a perspective view which shows an example of the uneven | corrugated shape employable as an uneven | corrugated structure area | region. It is a figure which shows roughly a mode that an uneven | corrugated structure area | region emits a diffracted light. It is a figure which shows schematically a mode that a fine uneven | corrugated structure area | region emits a diffracted light. It is a figure which shows roughly a mode that the solar cell module provided with the back surface protection sheet shown to FIG. 1 thru | or FIG. 3 is observed on a certain condition. It is a figure which shows schematically a mode that the solar cell module provided with the back surface protection sheet shown in FIG. 1 thru | or FIG. 3 is observed on the conditions different from FIG.

Hereinafter, the structure of the back surface protection sheet and the solar cell module using the same according to the embodiment of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a longitudinal sectional view of a solar cell module using the back surface protection sheet of the embodiment. As shown in FIG. 1, the back surface protection sheet 25 which forms a part of the module 1 is laminated on the back surface side of the solar cell module 1.

The solar cell module 1 includes a front plate 2, a filling layer 4, solar cells 10, and a back surface protection sheet 25, and is a device that generates power by receiving light rays. In addition, as a light ray, the light of artificial lighting, such as sunlight 20 and a room lamp, is normally employ | adopted.
In the solar cell module 1, sunlight 20 is reflected as incident light 12 incident on the solar cell 10 and reflected light 14 reflected and incident on the solar cell 10 is received and generated. In the solar cell module 1, the reflected light lost by the control of the back surface protection sheet 25 is reduced, and the power generation efficiency is improved more than ever.

  The front plate 2 is disposed on the forefront of the solar cell module 1 so that light rays are directly incident on the surface. The front plate 2 is made of a transparent material having a high light transmittance. Specifically, a resin sheet such as tempered glass or PEN (polyethylene naphthalate) is used. Further, the thickness of the front plate 2 is set to about 3 to 5 mm for tempered glass and several tens to several hundreds μm for a resin sheet.

  The light incident on the front plate 2 enters the filling layer 4. The filling layer 4 is laminated on the back surface side of the front plate 2 and has a role of sealing the solar battery cell 10. The filling layer 4 is made of a material having a high light transmittance so as to transmit the light incident from the front plate 2 and is made of, for example, EVA (ethylene vinyl acetate) having flame retardancy.

  The light transmitted through the filling layer 4 enters the solar battery cell 10. A plurality of the solar cells 10 are embedded in the filling layer 4 and have a function of converting light incident on the light receiving portion into electric power by the photoelectric effect. As the solar cell 10, a single crystal silicon type, a polycrystalline silicon type, a thin film silicon type, a CIGS (Cu · In · Ga · Se compound) type thin film type, or the like is used. A plurality of such solar cells 10 are connected to each other by electrodes (not shown), and the power generated by the electrodes is taken out to the outside.

The light transmitted through the filling layer 4 and the solar battery cell 10 enters the back surface protection sheet 25 disposed on the back surface of the solar battery module 1. The back surface protection sheet 25 has a function of partially reflecting incident light to the solar cell module 1. The light reflected by the back surface protection sheet 25 is further reflected at the interface between the front plate 2 and the atmosphere in the solar cell module 1 and reaches the light receiving surface of the solar cell 10 as reflected light 14, thereby the solar cell. It is converted into electric power by photoelectric conversion of the cell 10. As a result, the light utilization efficiency is improved.
FIG. 2 is a longitudinal sectional view showing a schematic configuration of the back surface protective sheet 25 of one embodiment. This back surface protection sheet 25 is configured by laminating a translucent insulating layer 34, a concavo-convex shape layer 42, a metal reflective layer 40, an adhesive layer 32, and a weather resistant layer 30 in this order.

  The transparent insulating layer 34 preferably has water resistance and weather resistance such as durability against ultraviolet rays. For example, polyethylene resin such as polyethylene terephthalate resin (PET resin), polypropylene resin, methacrylic resin, polymethyl Pentene resin, cyclic polyolefin resin, polystyrene resin, acrylonitrile- (poly) styrene copolymer (AS resin), acrylonitrile-butadiene-styrene copolymer (ABS resin), polyvinyl chloride resin, fluorine resin, Poly (meth) acrylic resin, polycarbonate resin, polyester resin, polyamide resin, polyimide resin, polyamideimide resin, polyarylphthalate resin, silicon resin, polysulfone resin, polyphenylene sulfide resin, polyether Sulfone-based resin, triethylene naphthalate resins, polyether imide resins, Epokishin resins, polyurethane resins, acetal resins, that are formed from a cellulose resin or the like.

Among the above-mentioned resins, polyimide resins, polycarbonate resins, polyester resins, fluorine resins, polylactic acid resins are those having high heat resistance, strength, weather resistance, durability, gas barrier properties against water vapor and the like. preferable.
Examples of the polyester-based resin include polyethylene terephthalate and polyethylene naphthalate. Among these polyester-based resins, polyethylene terephthalate is particularly preferable because it has a good balance between various functions such as heat resistance and weather resistance, and price.

  Examples of the fluororesin include polytetrafluoroethylene (PTFE), perfluoroalkoxy resin (PFA) made of a copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether, and a copolymer of tetrafluoroethylene and hexafluoropropylene (FEP). ), Copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether and hexafluoropropylene (EPE), copolymer of tetrafluoroethylene and ethylene or propylene (ETFE), polychlorotrifluoroethylene resin (PCTFE), ethylene and chlorotrifluoroethylene Copolymer (ECTFE), vinylidene fluoride resin (PVDF), vinyl fluoride resin (PVF), and the like. Among these fluororesins, polyvinyl fluoride resin (PVF) and a copolymer of tetrafluoroethylene and ethylene or propylene (ETFE) which are excellent in strength, heat resistance, weather resistance and the like are particularly preferable.

  Examples of the above-mentioned cyclic polyolefin-based resin include polymerizing cyclic dienes such as a) cyclopentadiene (and derivatives thereof), dicyclopentadiene (and derivatives thereof), cyclohexadiene (and derivatives thereof), norbornadiene (and derivatives thereof), and the like. And b) a copolymer obtained by copolymerizing the cyclic diene with one or more olefinic monomers such as ethylene, propylene, 4-methyl-1-pentene, styrene, butadiene, and isoprene. It is done. Among these cyclic polyolefin resins, cyclopentadiene (and derivatives thereof), dicyclopentadiene (and derivatives thereof) or norbornadiene (and derivatives thereof) such as polymers having excellent strength, heat resistance, and weather resistance are particularly preferred. preferable.

  In addition, as a forming material of the translucent insulating layer 34, the above-mentioned synthetic resins can be used alone or in combination. In addition, various additives and the like are mixed in the forming material of the translucent insulating layer 34 for the purpose of improving and modifying processability, heat resistance, weather resistance, mechanical properties, dimensional stability, and the like. Can do. Examples of the additive include a lubricant, a crosslinking agent, an antioxidant, an ultraviolet absorber, a light stabilizer, a filler, a reinforcing fiber, a reinforcing agent, an antistatic agent, a flame retardant, a flame retardant, a foaming agent, and an antifungal agent. And pigments. The forming method of the above-described translucent insulating layer 34 is not particularly limited, and known methods such as an extrusion method, a cast forming method, a T-die method, a cutting method, and an inflation method are employed.

  The light-transmitting insulating layer 34 may contain an ultraviolet stabilizer or a polymer having an ultraviolet stabilizing group bonded to a molecular chain. By this ultraviolet stabilizer or ultraviolet stabilizer, radicals generated by ultraviolet rays, active oxygen, and the like are inactivated, and the ultraviolet stability, weather resistance, and the like of the back protective sheet 25 can be improved. As the UV stabilizer or UV stabilizer, a hindered amine UV stabilizer or a hindered amine UV stabilizer having high stability to UV is preferably used.

  In the concavo-convex shape layer 42, when the concave / convex portion or both have a constant period, when the concavo-convex structure region is irradiated with sunlight, the concavo-convex structure region has a traveling direction of sunlight as incident light. Diffracted light is emitted in a specific direction. In particular, by covering the concavo-convex structure region with the metal reflective layer 40, high reflectance and high diffraction efficiency can be easily obtained.

The most representative diffracted light is first-order diffracted light. The exit angle β of the first-order diffracted light can be calculated from the following equation (1).
[Equation 1]
d = λ / (sin α−sin β) (1)

In this equation (1), d represents the period of the concave or convex structure, and λ represents the wavelength of incident light and diffracted light. Α represents the exit angle of 0th-order diffracted light, that is, specularly reflected light. In other words, the absolute value of α is equal to the absolute value of the incident angle of sunlight, and the exit angle of the specularly reflected light is symmetric with respect to the Z axis. Note that α and β are positive directions in the clockwise direction from the Z axis.
As is apparent from equation (1), the exit angle β of the first-order diffracted light changes according to the wavelength λ. That is, the uneven structure region has a function as a spectroscope. Therefore, when sunlight is white light, the color perceived by the observer changes when the observation angle of the concavo-convex structure region is changed. Further, the color perceived by the observer under a certain observation condition changes according to the period d.

As an example, it is assumed that the concavo-convex structure region emits first-order diffracted light in the normal direction. The normal direction here means a direction perpendicular to the surface when the uneven structure region is regarded as a surface. That is, the exit angle β of the first-order diffracted light is assumed to be 0 °. Assume that the observer perceives the first-order diffracted light. If the emission angle of the 0th-order diffracted light at this time is αN, equation (1) can be simplified to equation (2) below.
[Equation 2]
d = λ / sin αN (2)

As is clear from equation (2), in order for the observer to perceive a specific color, the wavelength λ corresponding to the color, the incident angle | αN | What is necessary is just to set so that the relationship shown in 2) may be satisfied.

  If the period d is made smaller than the wavelength of visible light (specifically, the period d is 400 nm or less), the first-order diffracted light is not emitted in the normal direction. That is, when the period of the concave part or convex part or both of the concave-convex shaped layer 42 in the present invention is 400 nm or less, the diffracted light component from the concave part or convex part or both is in the normal direction in the visible light region 400 to 700 nm. Can be avoided. In equation (2), even at 89 ° sunlight, 400 nm light will finally go near the normal direction, so under virtually all possible illumination conditions for virtually all visible wavelengths. Sufficient diffracted light is not generated in the normal direction from the concavo-convex structure region.

  Further, by setting the period of the concave portion or convex portion or both of the concave-convex shaped layer 42 to 200 nm or more and 400 nm or less, diffracted light can be similarly observed from a deep angle with respect to deep-angle sunlight. In addition, diffracted light is not generated under other conditions, and diffracted light is not recognized under general observation conditions. Therefore, when observed from the normal direction, the concavo-convex structure region can be more reliably reduced in reflection, and as a result, black is displayed under general observation conditions, and there is no fear of damaging the appearance.

Moreover, the uneven | corrugated shaped layer 42 recycles some sunlight which injects into the back surface protection sheet provided in the back surface side of the said photovoltaic cell by generating a diffracted light from a deep angle similarly with respect to sunlight of a deep angle. it can.
Since the uneven shape layer 42 is included in the back surface protection sheet, and the back surface protection sheet is provided in the solar cell module, diffracted light generated by the uneven surface layer is incident on the solar battery cell. Means that the generated diffracted light is reflected by the front plate disposed on the forefront of the solar cell module and is incident on the solar cell.

There is a difference in refractive index between the front plate and the atmosphere, and the emission angle β of the first-order diffracted light in the back protective sheet can be calculated from the following equation (3) obtained by modifying equation (1).
[Equation 3]
nd = λ / (sin α−sin β) (3)

In this equation (3), d represents the period of the concave or convex structure, λ represents the wavelength of incident light and diffracted light, and n represents the refractive index of the front plate. Α represents the exit angle of 0th-order diffracted light, that is, specularly reflected light. In other words, the absolute value of α is equal to the absolute value of the incident angle of sunlight, and the exit angle of the specularly reflected light is symmetric with respect to the Z axis. Note that α and β are positive directions in the clockwise direction from the Z axis.

There is a difference in refractive index between the front plate and the atmosphere, and the maximum wavelength at which the back surface protection sheet can reuse light as diffracted light when entering the solar cell at 90 ° from the atmosphere (refractive index of about 1). Thus, equation (3) can be simplified to equation (4) below.
[Equation 4]
d + nd = λ _max (4)

As an example, when a tempered glass having a concave or convex structure of the concavo-convex shape layer 42 is 600 nm and the front plate is made of tempered glass having a refractive index of 1.5, the back surface protection sheet is diffracted by the solar cell from equation (4). The maximum wavelength at which light can be reused as light is 1500 nm. When the solar cell is a silicon-based material, the silicon-based material has an absorption wavelength of less than 1300 nm at most, which is effective. Recognize.

The incidence of diffracted light generated in the normal direction is lower than the above, and it has a dark color such as black when observed from the normal direction. It is the said solar cell module provided with the said back surface protection sheet which can be reused.
The greater the height or depth of the convex or concave portion of the concavo-convex shape layer 42, the smaller the reflectance of the metal reflective layer 40 provided in the concavo-convex shape layer 42, and the closer to a dark color system such as black when viewed. As the height and depth become smaller, the luminance increases, and it is perceived by a dark color system such as black. Typically, it is desirable that the height and depth be ½ times or more and less than 1 time the center-to-center distance. Specifically, for example, when the center-to-center distance is 400 nm, a dark gray such as black is obtained by setting the height or depth to 200 nm or more, and black is obtained by setting the height or depth to 400 nm or more. While having an external appearance, the reflectance is drastically reduced, and the light to be reused is reduced.

It is desirable that the material for forming the uneven layer 42 has high adhesion to the transmissive insulating layer 34.
The material used for the concavo-convex shape layer 42 is preferably a polymer composition, and in addition to the polymer composition, for example, a curing agent, a plasticizer, a dispersant, various leveling agents, an ultraviolet absorber, an antioxidant, a viscosity modifier, A lubricant, a light stabilizer and the like may be appropriately blended.

  The polymer composition described above is not particularly limited. For example, poly (meth) acrylic resin, polyurethane resin, fluorine resin, silicon resin, polyimide resin, epoxy resin, polyethylene resin, polypropylene Resin, methacrylic resin, polymethylpentene resin, cyclic polyolefin resin, acrylonitrile- (poly) styrene copolymer (AS resin), polystyrene resin such as acrylonitrile-butadiene-styrene copolymer (ABS resin), Polyvinyl chloride resin, polycarbonate resin, polyester resin, polyamide resin, polyamideimide resin, polyaryl phthalate resin, polysulfone resin, polyphenylene sulfide resin, polyethersulfone resin, polyethylene naphthalate System resins, polyether imide resins, acetal resins, cellulose resins and the like, can be used as a mixture of these polymers alone or in combination.

  Examples of the polyol that is a raw material for the polyurethane resin include a polyol obtained by polymerizing a monomer component containing a hydroxyl group-containing unsaturated monomer, a polyester polyol obtained under conditions of excess hydroxyl group, and the like. These can be used alone or in admixture of two or more.

  Examples of the hydroxyl group-containing unsaturated monomer include (a) 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, allyl alcohol, homoallyl alcohol, Keihi Hydroxyl group-containing unsaturated monomers such as alcohol and crotonyl alcohol, (b) for example ethylene glycol, ethylene oxide, propylene glycol, propylene oxide, butylene glycol, butylene oxide, 1,4-bis (hydroxymethyl) cyclohexane, phenylglycidyl Dihydric alcohols or epoxy compounds such as ether, glycidyl decanoate, Plaxel FM-1 (manufactured by Daicel Chemical Industries, Ltd.) and, for example, acrylic acid, methacrylic acid, maleic acid, fumaric acid, Tonsan, and the like hydroxyl group-containing unsaturated monomers obtained by reaction of an unsaturated carboxylic acid such as itaconic acid. One or more selected from these hydroxyl group-containing unsaturated monomers can be polymerized to produce a polyol.

  The polyols described above are ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, tert-butyl acrylate, ethyl hexyl acrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, N-butyl methacrylate, tert-butyl methacrylate, ethyl hexyl methacrylate, glycidyl methacrylate, cyclohexyl methacrylate, styrene, vinyl toluene, 1-methyl styrene, acrylic acid, methacrylic acid, acrylonitrile, vinyl acetate, vinyl propionate, stearin Vinyl acid, allyl acetate, diallyl adipate, diallyl itaconate, diethyl maleate, vinyl chloride, vinylidene chloride, acrylamide, N-methylol acrylamide, N-butyl One or more ethylenically unsaturated monomers selected from xymethyl acrylamide, diacetone acrylamide, ethylene, propylene, isoprene and the like, and a hydroxyl group-containing non-functional group selected from the above (a) and (b) It can also be produced by polymerizing a saturated monomer.

  The number average molecular weight of a polyol obtained by polymerizing a monomer component containing a hydroxyl group-containing unsaturated monomer is from 1,000 to 500,000, preferably from 5,000 to 100,000. The hydroxyl value is 5 or more and 300 or less, preferably 10 or more and 200 or less, more preferably 20 or more and 150 or less.

  The polyester polyol obtained under the condition of excess hydroxyl group is (c), for example, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, neopentyl. Glycol, hexamethylene glycol, decamethylene glycol, 2,2,4-trimethyl-1,3-pentanediol, trimethylolpropane, hexanetriol, glycerin, pentaerythritol, cyclohexanediol, hydrogenated bisphenol A, bis (hydroxymethyl) Polyhydric alcohols such as cyclohexane, hydroquinone bis (hydroxyethyl ether), tris (hydroxyethyl) isosinurate, xylylene glycol, and (d) maleic acid, for example. Polybasic acids such as fumaric acid, succinic acid, adipic acid, sebacic acid, azelaic acid, trimetic acid, terephthalic acid, phthalic acid, isophthalic acid, and other polyvalent acids such as propanediol, hexanediol, polyethylene glycol, and trimethylolpropane It can be produced by reacting under conditions where the number of hydroxyl groups in the alcohol is greater than the number of carboxyl groups of the polybasic acid.

  The number average molecular weight of the polyester polyol obtained under the above hydroxyl group-excess conditions is 500 or more and 300,000 or less, preferably 2000 or more and 100,000 or less. The hydroxyl value is 5 or more and 300 or less, preferably 10 or more and 200 or less, more preferably 20 or more and 150 or less.

  The polyol used as the polymer material of the polymer composition is obtained by polymerizing the above-described polyester polyol and a monomer component containing the above-mentioned hydroxyl group-containing unsaturated monomer, and is a (meth) acryl unit. Etc. are preferred. If such a polyester polyol or acrylic polyol is used as a polymer material, the weather resistance is high, and yellowing of the reflective structure layer 15 can be suppressed. In addition, any one of this polyester polyol and acrylic polyol may be used, and both may be used.

  The number of hydroxyl groups in the above-described polyester polyol and acrylic polyol is not particularly limited as long as it is 2 or more per molecule, but if the hydroxyl value in the solid content is 10 or less, the number of crosslinking points decreases, and the solvent resistance Film properties such as heat resistance, water resistance, heat resistance and surface hardness tend to decrease.

  As a method of forming the concavo-convex shape layer 42, a plastic raw material is fed into a heating cylinder with a screw or a plunger, heated and fluidized, passed through a die at the tip to give a shape, and cooled and solidified with water or air, There is an extrusion method to make long products. Other examples include a pressing method using a die whose shape has been cut, a casting method, an injection molding method, a UV molding method, and the like. According to these methods, the front surface of the concavo-convex structure can be formed simultaneously with the sheet formation.

  The metal reflection layer 40 is a layer having a function of reflecting incident light. The material used for the metal reflective layer 40 is not particularly limited as long as it has reflectivity and can be deposited. For example, aluminum (Al), gold (Au), silver (Ag), platinum (Pt ), Nickel (Ni), tin (Sn), chromium (Cr), zirconium (Zr) and the like, and alloys thereof. Further, a high refractive index material such as zinc oxide or zinc sulfide may be included. Among these, aluminum has a high reflectance in the ultraviolet, visible, and near infrared regions, and it is possible to prevent internal erosion by forming an oxide film on the surface. Moreover, there exists an advantage that it has high water vapor | steam barrier property. Further, silver has an advantage that the reflectance is higher than that of aluminum in the visible and near infrared regions. Gold absorbs on the short wavelength side of the visible region, but has a higher reflectance than aluminum at wavelengths of 600 nm or longer. Furthermore, these three kinds of metals have an advantage that they are very difficult to be eroded, so that they are desirable as materials used for the metal reflection layer 40.

  When the metal reflection layer 40 is formed, the metal reflection layer 40 is formed by vapor-depositing a metal along the uneven layer 42. The vapor deposition means for the metal reflective layer 40 is not particularly limited as long as the metal can be vapor deposited without causing deterioration such as shrinkage and yellowing in the concavo-convex shape 42. (a) Vacuum vapor deposition, sputtering, ion Physical vapor deposition method (PVD method) such as plating method, ion cluster beam method, (b) Chemistry such as plasma chemical vapor deposition method, thermal chemical vapor deposition method, photochemical vapor deposition method, etc. A vapor phase growth method (Chemical Vapor Deposition method; CVD method) is employed. Among these vapor deposition methods, a vacuum vapor deposition method and an ion plating method that can form a high-quality reflective layer with high productivity are preferable.

  The metal reflection layer 40 may have a single layer structure or a multilayer structure of two or more layers. Thus, by making the metal reflective layer 40 into a multilayer structure, the deterioration of the concavo-convex shape layer 42 is reduced by reducing the heat load applied during vapor deposition, and the adhesion between the concavo-convex shape layer 42 and the metal reflective layer 40 is further reduced. Can be improved. At this time, a metal oxide layer may be provided on the metal film. Further, the deposition conditions in the physical vapor deposition method and the chemical vapor deposition method described above are appropriately designed according to the uneven shape layer 42, the resin type of the weather resistant layer 30, the thickness of the metal reflective layer 40, and the like.

  A general metal layer of the metal reflection layer 40 has a reflectivity that depends on the film thickness, and the thickness is preferably 40 nm or more. If the thickness is approximately 40 nm or more, the reflectivity is stable at a high reflectivity. On the other hand, when the thickness is smaller than 40 nm, a decrease in reflectance clearly appears. In order to exhibit an effect as a metal layer that can be visually recognized, a thickness of 5 nm or more is required. On the other hand, if the thickness is 100 nm or more, cracks that can be visually recognized occur.

  In the case of using the metal reflection layer 40 in the back surface protection sheet 25, it is preferable to perform a surface treatment on the surface of the concavo-convex shape layer 42, which is the deposition target surface of the metal reflection layer 40, in order to improve the tight adhesion and the like. Examples of such surface treatment include (a) corona discharge treatment, ozone treatment, low temperature plasma treatment using oxygen gas or nitrogen gas, glow discharge treatment, oxidation treatment using chemicals, and (b) primer. Examples of the coating treatment include undercoating, anchor coating, vapor deposition anchor coating, and the like. Among these surface treatments, corona discharge treatment and anchor coat treatment that improve the adhesive strength with the uneven shape 42 and contribute to the formation of a dense and uniform metal reflective layer 40 are preferable.

  Examples of the anchor coating agent used in the above-described anchor coating treatment include a polyester anchor coating agent, a polyamide anchor coating agent, a polyurethane anchor coating agent, an epoxy anchor coating agent, a phenol anchor coating agent, and a (meth) acrylic anchor. Examples thereof include a coating agent, a polyvinyl acetate anchor coating agent, a polyolefin anchor coating agent such as polyethylene aly polypropylene, and a cellulose anchor coating agent. Among these anchor coating agents, polyester anchor coating agents that can further improve the adhesive strength of the metal reflective layer 40 are particularly preferable.

The coating amount (in terms of solid content) of the above-described anchor coating agent is preferably 1 g / m ² or more and 3 g / m ² or less. When the coating amount of the anchor coating agent is less than 1 g / m ^{2, the} effect of improving the adhesion of the metal reflective layer 40 is reduced. On the other hand, when the coating amount of the anchor coating agent is more than 3 g / m ² , the strength, durability and the like of the back surface protection sheet 25 may be lowered.
In the above-mentioned anchor coating agent, a silane coupling agent for improving tight adhesion,
Various additives such as an anti-blocking agent for preventing blocking and an ultraviolet absorber for improving weather resistance can be appropriately mixed.

  The adhesive layer 32 desirably has good adhesion to the two layers in contact with the adhesive layer 32, and is used to supplement various properties such as durability and cushioning properties. As an example, a silicon resin or the like is used. It is done. By providing the adhesive layer 32, it is possible to compensate for performance that is insufficient with only the other layers. For example, a silicone resin is used to improve durability, cushioning properties, and the like. In particular, in the case of a solar cell module for outdoor use, the heat rise of the solar cell module during sunshine is remarkable, and the back surface protection sheet 25 made of a resin material is warped, which may cause a failure of the solar cell module. The weather resistant layer 30 is desirably formed of a material having high adhesion to the material forming the metal reflective layer 40.

As an example of a method for producing the back surface protection sheet 25 as described above, the uneven layer 42 is formed on the translucent insulating layer 34 by a UV forming method using a metal plate, and the metal reflective layer 40 is formed by vapor deposition or the like. Then, the weather resistant layer 30 is bonded via the adhesive layer 32.
In this way, the back surface protection sheet 25 of the present embodiment has a light-transmitting insulating layer 30 having one surface as a light incident surface and the other surface as a light emitting surface, and light. Metal reflective layer 40 provided on the exit surface side and having a reflection function of reflecting the light emitted from the light exit surface toward the translucent insulating layer 30 or appearing in a dark color system such as black depending on the observation direction, unevenness It has a shape layer 42 and a weather resistant layer 30 that protects from the back side.

  In the solar cell module having the back surface protection sheet 25 configured as described above, the light transmitted through the filling layer 4 and the solar cells 10 of the solar cell module 1 is distributed on the back surface of the solar cell module 1 as shown in FIG. A part of the incident light is incident on the rear surface protective sheet 25. Then, the light incident on the back surface protection sheet 25 is reflected to the solar cell 10 side by the metal reflective layer that is transmitted through the translucent insulating layer 30 and the adhesive layer 32 and laminated along the uneven shape 42 on the surface. The And the light recursed in the solar cell module 1 is received by the solar cell 10 to contribute to power generation, and the light use efficiency is improved.

  According to the back surface protective sheet 25 of the present embodiment, the uneven shape of the uneven layer 42 can be sufficiently filled with the adhesive layer 32 that is a layer that is in close contact with the metal reflective layer 40. In this regard, if the uneven shape 42 of the uneven layer is not firmly formed, the uneven shape cannot be sufficiently filled, delamination occurs, or a shape following the uneven shape is exposed on the surface. Therefore, the uneven shape of the uneven shape layer 42 can prevent delamination and entrainment of dust and dirt.

FIG. 3 is a cross-sectional view illustrating a schematic configuration of another embodiment of the back surface protection sheet. The back surface protection sheet 25 has a configuration in which a barrier layer 48 is bonded with an adhesive layer 32 between the adhesive layer 32 and the weather resistant layer 30. Here, the same components as those of the back surface protection sheet 25 of FIG. 2 are denoted by the same reference numerals, and detailed description thereof is omitted.
The barrier layer 48 refers to a material having high gas and water vapor permeability, and is preferably an aluminum alloy or the like. In practice, alloys such as copper (Cu), manganese (Mn), silicon (Si), magnesium (Mg), zinc (Zn), and nickel (Ni) are desirable, and are excellent in gas barrier properties such as oxygen and water vapor. Also, aluminum can prevent internal erosion by forming an oxide film on the surface.

FIG. 4 or FIG. 5 is a perspective view showing an example of a concavo-convex shape that can be employed in the concavo-convex structure region of the concavo-convex layer 42. Considering the case where the period d of the concave part or convex part 50 or both is in the region of 190 nm or more and 600 nm or less and the metal reflective layer is sufficiently formed, the transmittance becomes low and the uneven structure region is dark or black. Will have a dark color system. In particular, when they are arranged two-dimensionally at a constant cycle, the reflectance when observing from the normal direction is further reduced, and a dark color system such as black can be provided by the concavo-convex structure region.
The convex portions 50 shown in FIG. 4 or FIG. 5 are arranged in a lattice pattern in the x direction and the y direction substantially orthogonal to each other, but the convex portions 50 are arranged in a lattice pattern so as to intersect in different directions. Also good. In any case, the convex part 50 is dot-shaped.

  Moreover, the convex part 50 has the shape where the side surface has a taper (tapered shape), and therefore has a structure in which the cross-sectional area gradually increases or decreases in the vertical direction. Some may not have a tapered shape. The tapered shape is, for example, a semi-spindle shape, a cone shape such as a cone and a pyramid, or a truncated cone shape such as a truncated cone and a truncated pyramid. The convex portion 50 functions in substantially the same manner as a diffraction grating in which grooves (that is, grating lines) are arranged in a lattice shape corresponding to the arrangement.

FIG. 6 is a diagram schematically showing how the concavo-convex structure region of the concavo-convex layer 42 emits diffracted light. Here, the period d1 of the concave or convex structure of the concavo-convex shape 60 of the back surface protection sheet 25 is a case where it is larger than the wavelength λ of the sunlight 62, and the state in which the diffracted light emits the first-order diffracted light 66 is schematically shown. FIG.
As can be seen from equation (1), when the period d1 of the concave or convex structure of the diffraction grating is larger than the wavelength λ of the sunlight 62, when the sunlight 62 is irradiated from an oblique direction with respect to the interface, diffraction occurs. As shown in FIG. 6, the grating emits first-order diffracted light 66 at an emission angle β within a positive angle range.

FIG. 7 is a diagram schematically showing a state in which the concavo-convex structure of the concavo-convex shape layer 42 emits diffracted light. Here, the period d2 of the structure of the concave portion or the convex portion of the fine concavo-convex shape 70 is smaller than the wavelength λ of the sunlight 72, and is a principle diagram schematically showing how the diffracted light is emitted from the first-order diffracted light 76. .
As is clear from equation (1), when the period d1 of the concave or convex structure of the diffraction grating is smaller than the wavelength λ of the sunlight 72, when the sunlight 72 is irradiated from an oblique direction with respect to the interface, diffraction occurs. As shown in FIG. 7, the grating emits the first-order diffracted light 76 at an emission angle β within a negative angle range.

  6 and 7, when the period d of the concave-convex concave or convex structure is larger than the wavelength λ, the diffraction grating generates diffracted light in the normal direction. On the other hand, when the period d of the concave-convex concave or convex structure is smaller than the wavelength λ, the diffraction grating does not generate diffracted light in the normal direction, and the first-order diffracted light in the negative angle range. Inject.

  FIG. 8 is a diagram schematically showing a state in which the solar cell module provided with the back surface protection sheet shown in FIGS. 1 to 3 is observed under certain conditions. Moreover, FIG. 9 is a figure which shows schematically a mode that the solar cell module provided with the back surface protection sheet shown in FIG. 1 thru | or FIG. 3 is observed on other conditions. FIG. 8 is a view of the solar cell module 1 observed from the Z direction, and FIG. 1 can be said to be a view of the solar cell module 1 observed from the normal direction of the uneven surface.

The concavo-convex shape layer 42 provided in the back surface protection sheet 25 has a tapered shape. When such a structure is adopted, if the period d of the convex part or the concave part or both is sufficiently short, the reflectance for regular reflection is small and substantially does not emit diffracted light in the normal direction, and as a result When observed from the normal direction, it has a dark color system such as black.
FIG. 9 is a view of the solar cell module 1 observed from the Z direction, and can be said to be a view of the solar cell module 1 observed at a different angle than the normal direction which is the front of FIG.

As described above, since the diffraction grating emits the first-order diffracted light in the negative angular range from the normal direction, the irradiation light irradiated from the oblique direction with respect to the interface is observed in a dark color system from the normal direction which is the front. The back protective sheet 25 is a sheet having a blue, green or red wavelength of the emitted light.
Since the diffracted light of the back surface protection sheet 25 observed in FIG. 9 is reflected toward the light receiving surface of the solar battery cell at the interface of the light incident surface of the front plate 2, the light transmitted without being received by the light receiving surface is re-transmitted. Utilization can improve power generation efficiency.

Next, examples will be described. An implementation sample was produced using the configuration of FIG.
Aluminum was used as the material of the metal reflective layer 40, and vapor deposition was performed along the concavo-convex shape layer 42 by a vapor deposition method. In addition, six types of working samples 1 to 6 having a film thickness of aluminum that is the metal reflection layer 40 different from 50 nm, 70 nm, 90 nm, 95 nm, 100 nm, and 105 nm were prepared and observed for appearance problems.

After producing the working samples 1 to 6 from Table 1, if the aluminum has a thickness of about 100 nm or 105 nm in appearance judgment, cracks are generated so that the appearance can be recognized visually, and there is a problem in appearance. In addition, aluminum originally prevents the internal erosion by forming an oxide film on the surface, but it erodes from the cracked part to the inside and the corrosion progresses, so there is a problem in performance. is there. Therefore, the thickness of the metal reflective layer 40 needs to satisfy the range of 5 nm to 100 nm.

Next, working samples 7 to 12 were produced using the configuration of FIG. 2 or 3.
The working samples 7 to 12 are samples in which the Tg temperatures of the transparent insulating layer, the concavo-convex shape layer, and the weathering layer are changed, and the working samples 10 to 12 are samples in which aluminum foil is laminated.
The produced execution samples 7-12 were cut and the test piece of a magnitude | size of 200 mm (MD: Machine Direction roll flow direction) * 200 mm (TD: Transverse Direction roll perpendicular direction) was produced. Next, a marked line of 150 mm (MD) × 150 mm (TD) was drawn at the center of this test piece, and left in a thermostatic bath at 150 ° C. for 30 minutes. Then, it cooled, the length in the said marked line was measured, and the dimensional change rate was computed from the following equation (5).

Moreover, the shape of the test piece after a process was observed visually by external appearance, and the following reference | standard determined.
○: No deformation Δ: Slightly deformed ×: Deformed The prepared working samples 7 to 12 were cut to prepare a test piece having a size of 500 mm (MD) × 500 mm (TD). Then, the discoloration degree (ΔE) by a xenon weather meter acceleration test was measured with a color meter on the surface of the transparent insulating layer side. In the xenon weather meter accelerated test, Atlas Ci35 was operated at a black panel temperature of 63 ° C., a 340 nm illuminance of 0.25 W / m 2, and an irradiation time of 300 hours.

ΔE was calculated from Lab data by equation (6). Note that L is lightness, a is redness, and b is yellowness.
[Equation 6]
ΔE = √ {(L ₁ −L ₀ ) ² + (a ₁ −a ₀ ) ² + (b ₁ −b ₀ ) ² } (6)

L ₁ , a ₁ , b ₁ are values after exposure, and L ₀ , a ₀ , b ₀ are values before exposure.

In addition, the smaller the value of ΔE, the smaller the color change and the better the weather resistance. The weather resistance was determined according to the following criteria.
○: ΔE was 10 or less Δ: ΔE was 10 or more and less than 15.
X: ΔE was 15 or more

The produced working samples 7 to 12 were cut to produce a test piece having a size of 20 mm (MD) × 100 mm (TD), this test piece was suspended vertically, and the burner was used to squeeze the lower end of the test piece. With the distance of 10 mm until, the lower end of the test piece was indirectly flamed for 5 seconds. After completion of the flame contact, the combustion state of the flame contact portion of the test piece was visually observed and judged according to the following criteria.
○: not ignited ×: ignited

From Table 2, when the Tg temperatures of the concavo-convex shaped layers of the working samples 7 to 12 were larger than the other layers, the dimensional change rate was large and a state of being easily deformed was observed. However, if it is smaller than the other layers, the above problem does not occur and it can be said that it is relatively stable.
As for the weather resistance, the discoloration degree was high for the execution samples 7 to 9, and the discoloration degree was low for the execution samples 10 to 12. This is considered to be because the aluminum foil has a high barrier property and prevents discoloration.
Regarding the flame retardancy, all of the working samples 7 to 12 have good results, and it can be said that the configuration of FIG. 2 or 3 is relatively stable for the flame retardancy.

  The back surface protection sheet of the present invention can be used as a back surface protection sheet used in various optical devices such as display members and lighting devices. In particular, in the field of solar cells, it has excellent strength, weather resistance, heat resistance, water resistance, light resistance, chemical resistance, light reflectivity, light diffusibility and other fastnesses, and is extremely durable. It has high protection capability and is expected to be used to improve light efficiency.

DESCRIPTION OF SYMBOLS 1 Solar cell module 2 Front plate 4 Packing layer 10 Solar cell 12 Incident light (directly incident on a cell)
14 Reflected light (incident on cell)
20 Sunlight (light source)
25 Back surface protection sheet 30 Weather resistant layer 32 Adhesive layer 34 Translucent insulating layer 38 Weather resistant layer 40 Metal reflective layer 42 Concavity and convexity layer 48 Barrier layer 50 Convex portion 60 Concavity and convexity layer 62 Sunlight (light source)
64 0th-order diffracted light 66 1st-order diffracted light 70 Uneven shape layer 72 Sunlight (light source)
74 0th-order diffracted light 76 1st-order diffracted light d Period d1 of concave or convex structure d2 Period of concave or convex structure d2 shown in FIG. 6 Period of concave or convex structure shown in FIG.

Claims (8)

  In the solar cell module provided with solar cells that convert into electrical energy, a back surface protection sheet that reflects sunlight toward the solar cells is disposed on the side opposite to the light receiving surface of the solar cells, and the back surface protection The sheet includes a concavo-convex shape layer provided with a metal reflection layer, and the concavo-convex shape layer has a plurality of convex portions or a period of concave portions formed in a range from 190 nm to 600 nm.   2. The solar cell module according to claim 1, wherein the concavo-convex shape layer has a plurality of convex portions or concave portions having a period of 200 nm or more and 400 nm or less.   3. The solar cell module according to claim 1, wherein the concavo-convex shape layer has a depth or a height of a convex portion or a concave portion that is ½ times or more and less than 1 time of a period thereof.   A weather resistant layer, a metal reflective layer, a concavo-convex shape layer, and a light-transmissive insulating layer are sequentially provided from the rearmost surface side to the front surface side of the back surface protection sheet, and between the weather resistant layer and the metal reflective layer and / or metal reflective layer. The solar cell module according to claim 1, wherein at least one barrier layer is provided between the layer and the concavo-convex shape layer.   5. The solar cell module according to claim 1, wherein the metal reflective layer has a thickness of 5 nm to 100 nm.   The weather-resistant layer and the light-transmissive insulating layer are made of a thermoplastic resin, and the glass transition temperature of these thermoplastic resins is lower than the glass transition temperature of the resin constituting the concavo-convex shape layer. The solar cell module according to claim 4 or 5.   7. The solar cell module according to claim 4, wherein a thickness of the transparent insulating layer is 50 μm or more and 500 μm or less. A back surface protection sheet for a solar cell module, comprising a concavo-convex shape layer provided with a metal reflection layer, wherein the concavo-convex shape layer has a plurality of convex portions or concave portions having a period of 190 nm or more and 600 nm or less.

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