JP2021101490A - Backside protection sheet for solar battery module and solar battery module arranged by use thereof - Google Patents

Abstract

To provide a backside protection sheet for a solar battery module, which makes enough contribution to the increase in the power generation efficiency of a solar battery module and has a dark color layer superior in blocking resistance while it is a backside protection sheet for a solar battery module, of which the whole or part of a surface has a satisfactory hue of dark color in order to satisfy the demands of users for designability.SOLUTION: A backside protection sheet 6 for a solar battery comprises: a base material layer 61; and a dark color layer 62 which allows near infrared rays of 750-1500 nm in wavelength to pass therethrough. The dark color layer 62 includes a resin component, a dark color pigment, and a transparent inorganic filler. In the dark color layer 62, the content of the transparent inorganic filler is 0.5-5 pts.mass to 100 pts.mass of the resin component. The transparent inorganic filler has an average particle diameter which is 50-150% of a thickness of the dark color layer 62.SELECTED DRAWING: Figure 1

Description

The present invention relates to a back surface protective sheet for a solar cell module and a solar cell module using the same.

In recent years, due to growing awareness of environmental issues, solar cells have been attracting attention as a clean energy source. Generally, a solar cell module constituting a solar cell has a structure in which a transparent front substrate, a sealing material, a solar cell element, a sealing material, and a back surface protective sheet are laminated in this order from the light receiving surface side, and sunlight is a solar cell. It has a function of generating electricity by incident on the element.

Generally, most of the encapsulants for solar cell modules are transparent or translucent. Therefore, when the solar cell module is viewed from the transparent front substrate side, the gaps where the solar cell elements are not arranged can be seen. The color of the back surface protective sheet is visually recognized in a plan view from the surface side on which the solar cell element is arranged. Further, the surface of the solar cell element is often black or a dark color close to it. In particular, the surface of most thin-film solar cell elements, whose demand has been increasing in recent years, is black or a dark color close to it.

Therefore, the back surface protective sheet for the solar cell module is often required to have a dark appearance from the viewpoint of design. As a dark-colored pigment that can be used to impart a dark-colored appearance to the resin base material constituting the back surface protective sheet, carbon black can be mentioned as a general-purpose pigment. However, although carbon black is excellent in design when a black appearance is required, on the other hand, it absorbs near infrared rays well, so that the back surface protective sheet using this and the sun using the back surface protective sheet are further used. There is a problem that the temperature of the battery module is raised, which lowers the power generation efficiency of the solar cell module.

Therefore, a back surface protective sheet for a solar cell module in which a dark ink layer is formed by using a dark organic pigment that transmits near infrared rays without absorbing them has been developed. According to this, the near-infrared light that has passed through the dark color ink layer can contribute to the power generation of the solar cell module while maintaining the appearance of the dark color that is preferable in terms of design. Any of the efficiencies can be preferably maintained at a level (Patent Document 1).

In many cases, the back surface protective sheet having the dark color layer as described above is used at any stage of the manufacturing process from the application of the dark color ink to the incorporation into the solar cell module to the final usage form. The dark layer is wound into a roll while being exposed on the outermost surface. Therefore, in the above-mentioned back surface protective sheet having a dark color layer, in addition to contributing to designability and power generation efficiency, the dark color layer formed on the surface thereof is excellent in blocking resistance in order to improve productivity. It is required to have sex.

In order to improve the blocking resistance of the resin base material, it is generally carried out that the surface layer contains an inorganic filler such as titanium dioxide or carbon black (see Patent Document 2). However, in the back surface protective sheet having a dark appearance as described above, when the dark layer contains white titanium dioxide having a particle size and concentration sufficient to contribute to the improvement of blocking resistance, the dark color layer may contain white titanium dioxide. As described above, carbon black is not preferable because it directly causes a decrease in design and may reduce power generation efficiency.

International Publication No. 2016/205641 JP-A-2015-170735

The present invention impairs these preferable effects in the back surface protective sheet for a solar cell module, which can maintain both the design property related to the dark appearance of the solar cell module and the power generation efficiency at a preferable level. It is an object of the present invention to provide a back surface protective sheet for a solar cell module having excellent productivity by improving blocking resistance.

The present inventors have found that the above problems can be solved by incorporating a transparent inorganic filler having a predetermined particle size and refractive index into the dark color layer, and have completed the present invention. Specifically, the present invention provides the following.

(1) A base material layer and a dark color layer that transmits near infrared rays having a wavelength of 750 nm or more and 1500 nm or less are provided, and the dark color layer contains a resin component, a dark color pigment, and a transparent inorganic filler. The content of the transparent inorganic filler contained in the dark color layer is 0.5 parts by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the resin component, and 0.5 parts by mass with respect to 100 parts by mass of the resin component. A back surface protective sheet for a solar cell having a portion or more and 5 parts by mass or less, and an average particle size of the transparent inorganic filler having a size of 50% or more and 150% or less with respect to the thickness of the dark color layer.

(2) The back surface protective sheet according to (1), wherein the difference between the refractive index of the transparent inorganic filler and the refractive index of the resin component is 0.20 or less.

(3) The back surface protective sheet according to (1) or (2), wherein the transparent inorganic filler is transparent silica.

(4) The back surface protective sheet according to any one of (1) to (3), wherein the base material layer has a reflectance of near infrared rays of 750 nm or more and 1500 nm or less of 50% or more.

(5) The back surface protective sheet according to any one of (1) to (4), wherein the dark color layer is formed on a part of the surface surface of the base material layer to form a continuous repeating pattern.

(6) The back surface protective sheet according to any one of (1) to (5) is a solar cell module laminated on another resin base material, and is a transparent inorganic filler contained in the dark layer. A solar cell module in which the difference between the refractive index and the refractive index of the resin base material laminated on the surface of the dark color layer is 0.20 or less.

According to the present invention, in the back surface protective sheet for a solar cell module, which can maintain both the design property related to the dark appearance of the solar cell module and the power generation efficiency at a preferable level, these preferable effects are described above. By improving the blocking resistance without impairing the above, it is possible to provide a back surface protective sheet for a solar cell module having excellent productivity.

It is sectional drawing which shows typically the layer structure of embodiment of the back surface protection sheet which concerns on this invention. It is sectional drawing which shows typically the layer structure which concerns on other embodiment of the back surface protection sheet which concerns on this invention. It is sectional drawing which shows an example of the layer structure of the solar cell module using the back surface protection sheet of this invention.

<Solar cell module>
First, the solar cell module 1 that can be obtained by using the back surface protective sheet 6 of the present invention will be described. FIG. 3 is a schematic view showing the layer structure of the solar cell module 1. In the solar cell module 1, the transparent front substrate 2, the front sealing material layer 3, the solar cell element 4, the back sealing material layer 5, and the back surface protective sheet 6 of the present invention are laminated in this order from the light receiving surface side of the incident light 7. It is a configuration. Further, the solar cell module 1 can be manufactured by sequentially laminating the above-mentioned members and integrating them by, for example, vacuum thermal laminating. The lamination temperature at this time is preferably in the range of 130 ° C. to 190 ° C.

<Back side protective sheet>
The back surface protective sheet 6 has a two-layer structure in which a dark color layer 62 is formed on the surface of the base material layer 61, which is a minimum essential configuration requirement. The dark color layer 62 may be formed on the entire surface of the base material layer 61 (see FIG. 1), or may form a patterning pattern by being formed on a part of the surface of the base material layer 61. Good (see Figure 2). When the dark layer 62 is formed on the entire surface of the base material layer 61, the dark layer 62 can be a dark adhesive layer, can be formed as a dark primer layer, or is a dark layer. The surface of 62 may be further provided with another adhesion improving layer that imparts sufficient adhesion to other members.

As shown in FIG. 2, the back surface protective sheet 6 is formed by selectively forming a dark color layer 62 only on a part of the base material layer 61 in order to apply a patterning pattern, for example, from the viewpoint of designability. In this case, a dark ink is partially applied to the surface of the base material layer 61 to form such a dark layer 62, and then the transparent adhesive layer 63 is coated with a transparent adhesive. By further laminating the transparent adhesive layer 64 via the transparent adhesive layer 63, it is possible to manufacture a back surface protective sheet having an appearance having a patterning pattern. The transparent adhesive layer 64 has a function of improving the adhesiveness between the back surface sealing material layer 5 using a polyolefin such as ethylene-vinyl acetate alcohol copolymer resin (EVA resin) or polyethylene and the back surface protective sheet 6. .. Further, the transparent adhesive layer 64 is required to transmit near infrared rays reflected by the base material layer 61, and to be transparent or translucent due to the demand for design. From this point of view, it is preferable to use a polyolefin resin such as polyethylene resin or polypropylene resin, or polyethylene terephthalate (PET) for the transparent adhesive layer 64.

In the case of the above layer structure, the dark color layer 62 is not the layer exposed on the outermost surface of the back surface protective sheet 6 at the completion stage of the back surface protective sheet 6, but the blocking resistance is improved in any process of the manufacturing stage. It is possible to enjoy the merits of the above and the effect of maintaining the design, which is within the scope of the back surface protective sheet of the present invention. That is, in the back surface protective sheet of the present invention, the dark color layer only needs to be laminated on the surface of the base material layer, and further, on the surface thereof, another other that does not interfere with the above-mentioned effects that the present invention can exert. It is a back surface protective sheet that is naturally within the scope of the present invention even if a transparent layer or the like is further laminated. Hereinafter, unless otherwise specified, the back surface protective sheet of the present invention will be described by taking the embodiment shown in FIG. 1 as a specific example.

[Dark color layer]
The dark color layer 62 is formed by applying a dark color ink containing a resin component, a dark color pigment, and a transparent inorganic filler, which will be described in detail below, to the surface of the resin sheet and forming a coating film from the applied dark color ink. be able to. The dark color ink is preferably a two-component type in which the main agent and the curing agent are mixed immediately before use.

The dark color layer 62 is a layer that imparts a dark color appearance to the back surface protective sheet 6 in terms of design. Here, the "dark color" in the present specification means a "color" in which ^{the range of the L *} value in the color coordinates is in the following specific range, and black is naturally included in this. ^{Specifically, the specific range means a range in which the L *} value measured under the conditions of a D65 light source and a 10 ° viewing angle is 30 or less, preferably 10 or less, in accordance with JIS-Z8722: 2009. , The color in this range is referred to as "dark color" in the present specification.

Further, the dark color layer 62 is formed so as not only to impart a dark color design to the back surface protective sheet 6 as described above, but also to be a layer that transmits near infrared rays in order to suppress the temperature rise of the solar cell module. Has been done. Regarding the transmittance of light rays in a predetermined wavelength range, an ultraviolet visible spectrophotometer (UV visible spectrophotometer UV manufactured by Shimadzu Corporation) is measured by a measurement method according to JIS K7375-2008 (plastic-total light transmittance and total light reflectance). It can be measured using -2550). In the present specification, "transmitting" light in a certain wavelength range means that the light transmittance in the wavelength range measured by the above measuring method (JIS K7375-2008) is 10 unless otherwise specified. It is said that it is more than%. More specifically, the measurement of the light transmittance of the dark color layer 62 can be performed by, for example, the following method. Infrared transmissive dark ink 5 g / m ² containing a curing agent is gravure-coated on white PET (188 μm), polyethylene (60 μm) is laminated on it, and aging treatment at 45 ° C or higher and 55 ° C or lower for 168 hours. To create a back surface protective sheet by overheating and curing. Then, the polyethylene and the white PET of the back surface protective sheet are peeled off, and a measurement sample of the transmittance of the solution in which the dark color layer is dissolved using methyl ethyl ketone is prepared. The measurement sample is injected into a quartz glass cell and used with a spectrophotometer (for example, JASCO Corporation, ultraviolet spectrophotometer "V-670" or Hitachi High Technologies Co., Ltd., "U-4100") with a wavelength of 300 nm or more. The content of the brown pigment in the dark layer can be estimated by measuring the transmittance (%) of light at 1200 nm and determining the transmittance of light having a wavelength of 425 nm and light having a wavelength of 675 nm, respectively.

(Resin component)
The resin component contained in the dark layer 62 is preferably a crosslinked resin or a fluoroacrylic resin in which the resin component containing polycarbonate polyurethane is crosslinked with an isocyanate-based curing agent. Further, it is more preferable that the resin component constituting the crosslinked resin is glycol-modified polycarbonate polyurethane. By using glycol-modified polycarbonate polyurethane as the resin component, the flexibility of the dark color layer 62 is increased, and the adhesiveness and impact resistance of the same layer are improved.

(Dark pigment)
As the dark pigment, a pigment that transmits near infrared rays having a wavelength of 750 nm or more and 1500 nm or less can be used. For example, oxazine pigments, benzimidazolone pigments, pyrrole pigments, quinacridone pigments, azo pigments, perylene pigments, dioxane pigments, isoindolinone pigments, induslen pigments, quinophthalone pigments, perinone pigments. , Organic pigments such as phthalocyanine pigments can be mentioned.

As the oxazine-based organic pigment, for example, violet 23 (molecular weight 589), CI direct violet 37 (molecular weight: 789), a dioxazine-based compound as described in JP-A-2003-105217, and the like can be used. .. Oxazine-based organic pigments have high UV resistance and adhesiveness, and can be preferably used as pigments contained in dark-colored inks.

Among the pigment components, it is preferable that the pigment component contains a dark pigment composed of a brown pigment and a phthalocyanine pigment. By using a brown pigment and a phthalocyanine pigment, it is possible to obtain a sufficient color even when the thickness of the dark layer is reduced. Therefore, even when the dark color layer is laminated only on a part of the surface, the step with the surface on which the dark color layer is not laminated is small. Therefore, a plurality of layers can be laminated with a small amount of transparent adhesive, and a low-cost and highly productive back surface protective sheet for a solar cell module can be obtained. As the above-mentioned "dark pigment composed of a brown pigment and a phthalocyanine pigment", in detail, the pigment used for the "infrared transmissive dark color ink" disclosed in Patent Document 1 is also applied to the back surface protective sheet of the present invention. It can be preferably used.

The content of the above-mentioned "dark pigment composed of a brown pigment and a phthalocyanine pigment" in the dark layer 62 can be specified by the light transmittance of a specific wavelength in the light transmittance test. Further, in order to make the content of the brown pigment such as the benzimidazolone pigment and the content of the phthalocyanine pigment preferable in terms of design and infrared transmission, benzimidazolone contained in the dark color layer is required. Brown pigments such as system pigments and phthalocyanine pigments are 80% by mass or more in the total amount of pigment components, and the light transmission rate at a wavelength of 425 nm in the light transmission rate test of a dark color layer is 5% or more and 30% or less. , The transmittance of light having a wavelength of 675 nm is preferably 4% or more and 20% or less. The phthalocyanine pigment has a property of transmitting a certain amount of light having a wavelength of 425 nm and not transmitting light having a wavelength of 675 nm. A brown pigment such as a benzimidazolone pigment has a property of transmitting a certain amount of light having a wavelength of 675 nm and a property of not transmitting light having a wavelength of 425 nm. Therefore, by specifying the transmittance of light having a wavelength of 425 nm and the transmittance of light having a wavelength of 675 nm in the light transmittance test, the content of brown pigments such as benzimidazolone pigments and the content of phthalocyanine pigments are contained. The content ratio with the amount can be specified.

The content of the dark pigment in the dark layer 62 is preferably 20 parts by mass or more and 50 parts by mass or less, and more preferably 35 parts by mass or more and 45 parts by mass or less with respect to 100 parts by mass of the resin component. By setting the content of the dark pigment in this range, the color tone can be stabilized. Further, if the dark color layer 62 is formed by a near-infrared transmissive dark color ink containing a pigment component containing the above-mentioned field "brown pigment and phthalocyanine pigment", a sufficient color can be obtained even in a thin dark color layer. It is possible. Therefore, even when the dark color layer is laminated only on a part of the surface, the step with the surface on which the dark color layer is not laminated is small. Therefore, it is possible to laminate with a small amount of transparent adhesive, and it is possible to obtain a back surface protective sheet for a solar cell module with low cost and high productivity.

(Transparent inorganic filler)
In addition to the resin component and the dark pigment, the dark layer 62 further contains a transparent inorganic filler mainly for improving blocking resistance. "Transparent" in the present specification means that "transparent light rays can be transmitted", and more specifically, the light transmittance by the above measuring method (JIS K7375-2008) at a wavelength of 400 nm or more and 750 nm or less is determined. It shall mean that it is at least 80% or more. By limiting the filler added to improve the blocking resistance to such a transparent one, the blocking resistance in the dark layer 62 is improved without impairing the design property related to the dark appearance required for the dark layer 62. Can be made to.

The transparent inorganic filler in the present invention includes all inorganic fillers having such "transparent" optical properties. As the transparent inorganic filler added to the dark color layer 62, specifically, transparent silica having the above-mentioned range of transparency can be preferably used.

Regarding the particle size of the transparent inorganic filler that can be used for the dark color layer 62, the average particle size is 50% or more and 150% or less, preferably 80% or more, based on the thickness of the dark color layer 62 to which the transparent inorganic filler is added. Those having a size of 100% or less can be used. The content of the transparent inorganic filler in the dark color layer 62 may be 0.5 parts by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the resin component in the dark color layer, and is 1 part by mass or more and 2.5 parts by mass. It is preferably less than or equal to a portion. The thickness of the dark color layer 62 in the back surface protective sheet 6 is not limited to a specific range, but is generally in the range of approximately 2 μm or more and 8 μm or less. For example, when the thickness of the dark layer 62 is 5 μm, a transparent inorganic filler having an average particle size of 2.5 μm or more, preferably 4 μm or more is contained in the dark layer within the above content range to form the dark layer 62. The blocking resistance on the surface can be improved to a sufficiently preferable range. On the other hand, if the average particle size exceeds 150% of the thickness of the dark layer 62, the demerit of lowering the adhesion to other members at the time of integration as a solar cell module outweighs the merit of improving blocking resistance, which is not preferable. Regarding the thickness of the dark color layer 62, which is a prerequisite for defining the average particle size of the transparent inorganic filler in the above, it is assumed that the thickness of the same layer is uniform, but for example, the particle size is large. When there is a portion whose thickness is locally increased following the surface of the transparent inorganic filler, the thickness of the portion having a uniform thickness excluding that portion is considered to be the thickness of the dark color layer 62. And. Regarding the thickness of the dark color layer 62 in the back surface protective sheet 6, after cutting the back surface protective sheet 6 and embedding it in a resin, a test piece is prepared using a microtome, and the cross section is formed by an optical microscope or SEM (Scanning Electron). It can be measured by observing with a microscope (scanning electron microscope). In the present invention, the thickness measured by this measuring method is defined as the thickness of the dark layer.

Further, it is preferable that the refractive index of the transparent inorganic filler is in a specific range. Specifically, the difference from the refractive index of the above resin component forming the dark color layer 62 is preferably 0.20 or less, and more preferably 0.05 or less. As a result, the visibility of the transparent inorganic filler dispersed in the dark color layer 62 is further lowered, and the back surface protective sheet 6 can be provided with further excellent designability from the viewpoint of maintaining the designability of the dark color. Regarding the refractive index of the resin component of the dark color layer 62 in the back surface protective sheet 6, for example, the dark color layer 62 was dissolved with a soluble solvent to extract a transparent inorganic filler, and then the solvent component was further volatilized and left. The resin component can be made effective again, and its refractive index can be specified by measuring it with a measuring machine such as a Carnew precision refractometer (KPR-30) manufactured by Shimadzu Corporation.

Regarding the refractive index of the transparent inorganic filler, in the solar cell module 1 formed by using the back surface protective sheet 6, other resin groups such as another back surface encapsulant layer 5 laminated on the surface of the dark color layer 62. The difference from the refractive index of the material is preferably 0.20 or less, and more preferably 0.05 or less. As a result, similarly to the above, the visibility of the transparent inorganic filler dispersed in the dark color layer 62 and the transparent inorganic filler partially exposed from the surface of the dark color layer 62 is lowered, and the design of the dark color is maintained. Therefore, it is possible to impart even better design to the back surface protective sheet 6. For example, the refractive index of EVA resin, which is generally used as a sealing material for a solar cell module, is about 1.49. When it is assumed that the transparent inorganic filler is laminated with the sealing material made of this EVA resin, the refractive index of the transparent inorganic filler is preferably 1.29 or more and 1.69 or less, and 1.44 or more and 1.54. It is more preferable that it is as follows.

[Base layer]
Examples of the resin sheet constituting the base material layer 61 include fluororesins such as PTFE (polytetrafluoroethylene) and ETFE (tetrafluoroethylene / ethylene copolymer), poly (meth) acrylic resins, and PET (polyester terephthalate). ) And other resin sheets such as polyester resin can be preferably used. Here, in the back surface protective sheet 6, the base material layer 61 is assumed to be the outermost layer when integrated as the solar cell module 1, and therefore has high weather resistance, barrier property, and hydrolysis resistance. Is required. From such a viewpoint, among the above, it is particularly preferable to use a fluorine-based resin typified by ETFE or a polyester-based resin typified by PET.

The base material layer 61 is further preferably a layer having a near-infrared reflectance of 50% or more in a wavelength range of 750 nm or more and 1500 nm or less, more preferably 60% or more of the same reflectance, and the same reflection. It is more preferable that the rate is 80% or more. In order to obtain the above-mentioned reflective layer, the base material layer 61 is a white resin composed of a resin sheet containing a white pigment or a resin sheet on which a coat layer (coating film or printing film) containing a white pigment is formed. It is preferably a layer. By forming the base material layer 61 as such a white resin layer, in the solar cell module 1, the incident light including near infrared rays transmitted through the dark color layer 62 of the back surface protective sheet 6 is reflected in the base material layer 61. By making it possible to reflect light and enter the solar cell element 4, it is possible to contribute to the improvement of the power generation efficiency of the solar cell module 1. In the present specification, "reflecting" light in a certain wavelength range or "having reflectivity" with respect to the light is measured by the above-mentioned measuring method (JIS K7375-2008) unless otherwise specified. It is also said that the reflectance in the wavelength range is 40% or more, preferably 60% or more, more preferably 80% or more. Further, in the present specification, "reflectance is equal to or higher than a specific value" in a predetermined wavelength range means that the reflectance in the wavelength range is at least the specific value or higher at any wavelength in the wavelength range. It shall mean that.

As the base material layer 61, in order to reflect near infrared rays particularly well, it is preferable to use a white resin layer containing a white pigment having a particle size of 0.5 μm or more and 1.5 μm or less, and the particle size is 0.8 μm or more. It is more preferably 2 μm or less. Further, in the base material layer 61, it is preferable that the particles of the white pigment having a particle size of 0.8 μm or more and 1.2 μm or less are 80% by mass or more of the particles of the total white pigment. By setting the particle size and distribution ratio of the white pigment in the above range, the white resin layer efficiently reflects near infrared rays, so that the white pigment can further contribute to the improvement of the power generation efficiency of the solar cell module.

A typical example of a white pigment having a particle size of 0.5 μm or more and 1.5 μm or less is titanium oxide, and it is preferable to use titanium oxide as the white pigment in the present invention as well. Here, titanium oxide also includes surface-treated titanium oxide.

Titanium hydroxide-containing raw material is used as a raw material, and an aluminum compound of 0.1% by mass or more and 0.5% by mass or less in terms of aluminum oxide and 0.1% by mass or more and 0.5% by mass in terms of potassium carbonate are added thereto. It can be produced by adding the following potassium compound and a zinc compound of 0.2% by mass or more and 1.0% by mass or less in terms of zinc oxide, drying and roasting.

Examples of the method for producing the reflective base material layer 61 include a method of forming a coat layer containing a white pigment on a resin sheet and a method of kneading the white pigment into the resin sheet. All of them are not particularly limited and can be produced by a conventionally known method.

[Method of forming dark layer]
In the dark color layer, a near-infrared transmissive dark color ink is applied to the surface of the resin sheet to form a coating film, and after the solvent contained in the coating film is evaporated, the resin component and the curing agent contained in the coating film are combined. Can be formed by subjecting to a cross-linking reaction and curing.

As a method of applying the near-infrared transmissive dark color ink to the surface of the resin sheet, a conventionally known method can be used without particular limitation. Examples of such a coating method include a printing method, a coating method using a gravure coater, a roll coating method, a spray coating method, a dip coating method, a solid coating method, and a brush coating method.

As a method for evaporating the solvent contained in the coating film, a conventionally known method can be used without particular limitation. Examples of such an evaporation method include a heating method, a vacuum drying method, a hot air drying method, and a natural drying method, but the method is not particularly limited. The conditions for evaporating the solvent contained in the coating film may be appropriately set according to the solvent used, but the heating time and heating temperature may be in the range of 50 to 120 ° C. for 1 to 5 minutes. It is preferable, and it is more preferably 70 to 100 ° C. for 2 minutes. By heating in this way, preferable blocking resistance and adhesiveness are exhibited. The coating film obtained by evaporating the solvent is subjected to curing for sufficient cross-linking reaction. The curing conditions may be appropriately set according to the type of the main agent and the curing agent used, and examples thereof include leaving at 40 to 50 ° C. for 3 to 4 days.

When the solvent is evaporated and removed from the coating film, the resin component, the curing agent, and other additives added to the near-infrared transmissive dark ink remain on the surface of the resin sheet to form the coating film. This coating film cures to form a dark layer.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples and the like.

In order to confirm the development of favorable effects related to the blocking resistance and designability of the back surface protective sheet of the present invention, the near-infrared transmissive dark color ink for testing was adjusted by the method shown below, and the back surface of each example comparative example was prepared. A protective sheet sample was produced.

<Near infrared transmissive dark color ink>
[Main agent]
An aliphatic polycarbonate diol (50 parts by mass), 1,6 hexanediol (70 parts by mass), and 1,8-octanediol having a number average molecular weight of 1000 are placed in a round bottom flask equipped with a stirrer, a thermometer, and a nitrogen gas introduction tube. (30 parts by mass), isophorone diisocyanate (IPDI) (176.6 parts by mass), trimethylolpropane (TMP) adduct modified product of isophorone diisocyanate (IPDI) (10 parts by mass), and ethyl acetate (333.6 parts by mass). ) Was charged, and the mixture was heated and ^{recirculated until the absorption of 2270 cm -1} isocyanate disappeared in the infrared absorption spectrum under the introduction of nitrogen gas. Was adjusted. In this example, the glycol modification amount is the mass (mass ratio%) of the alkylenediol compound (in this example, a mixture of 1,6 hexanediol and octanediol) with respect to the total component mass of the main resin component. The amount of IPDI modification refers to the mass of the modified isocyanate compound (in this example, the trimethylolpropane (TMP) adduct-modified product of isophorone diisocyanate (IPDI)) with respect to the total component mass of the resin component of the main agent. Mass ratio%). The total amount of 1,6-hexanediol and 1,8-octanediol added so that the amount of glycol modification is 10% and the amount of IPDI modification is 3%, and the amount of isophorone diisocyanate (IPDI) trimethylolpropane (TMP) adduct. The amount of the modified product added was appropriately adjusted.
[Curing agent]
A curing agent composed of a nurate form (40 parts by mass) of hexamethylene diisocyanate (HDI) and a trimethylolpropane (TMP) adduct modified product (60 parts by mass) of isophorone diisocyanate (IPDI) was prepared. The NCO / OH ratio, which is the ratio of the NCO value of the polyisocyanate compound to the OH value of the crosslinkable main resin, was set to 1.0.
[Dark pigment]
The content ratio of "Benz imidazolone pigment (PigmentBrown25, particle size 0.08 μm)" and "amorphous phthalocyanine pigment blue (PigmentBlue15, particle size 0.15 to 0.20 μm)" is 52.5: Using a dark pigment of 47.5, the pigment component was adjusted to be 40 parts by mass with respect to 100 parts by mass of the resin component of the main agent.
[Filler]
Filler 1: Transparent silica (total light transmittance 80% or more) (Silicia 530 manufactured by Fuji Silysia Chemical Ltd.), average particle size 4 μm, refractive index 1.46.
Filler 2: Transparent silica (total light transmittance 80% or more) (Silicia 430 manufactured by Fuji Silysia Chemical Ltd.), average particle size 2 μm, refractive index 1.46.
Filler 3: Thermosetting resin spherical fine particles made from melamine resin and benzoguanamine resin (total light transmittance less than 60%) (Eposter manufactured by Nippon Catalyst Co., Ltd.)
[Solvent]: Ethyl acetate

The main agent, the curing agent, the pigment, and any of the fillers 1 to 3 are dissolved in the solvent, and the near-infrared transmissive dark color inks used in the comparative examples of each example are as shown in Table 1. Created.

<Blocking resistance test>
Each back surface protective sheet sample prepared by the following method using a near-infrared transmissive dark color ink for testing was tested for blocking resistance by the following method, and the blocking resistance was evaluated based on the measurement results. All test pieces are 15 mm wide.
[Preparation of backside protective sheet sample]
As shown in Table 1, the surface of the white PET (white PET manufactured by Toray Industries, Inc., 188 μm) film was coated with a near-infrared transmissive dark color ink for testing with a bar coater for each sample. The ink was dried at 120 ° C. for 2 minutes to form a dark layer on the surface of the substrate. The amount of the ink applied was such that the thickness of the dark layer in each sample was the thickness shown in Table 1. Then, a sample for evaluation of blocking resistance was prepared by curing white PET (white PET manufactured by Toray Industries, Inc., 188 μm) at 50 ° C. for 3 days in contact with the surface of the dark layer immediately after drying. The blocking resistance test was conducted by a method of evaluating the blocking state by peeling off the overlapped portion of each blocking resistance evaluation sample, and evaluated according to the following criteria.
[Evaluation criteria]
◯: Sheets spontaneously peel off without transfer of dark color layer Δ: There is some adhesion feeling when peeling between base materials without transfer of dark color layer ×: There is transfer of dark color layer and / or between base materials There is a close contact feeling when peeling off

<Adhesion test>
Adhesion tests were performed on each back surface protective sheet sample prepared by the same method as described above using inks 1 to 5 by the following method, and the adhesion was evaluated based on the measurement results. All test pieces are 15 mm wide.
Adhesion tests were conducted according to ASTM D3359 and JIS 5400, and the adhesion was evaluated according to the following criteria. The results are shown in Table 1 below as "adhesion".
[Evaluation criteria]
◯: 0% coating peeling Δ: Coating peeling of more than 0% and 15% or less ×: Coating peeling of more than 15%

<Design evaluation test>
For each back surface protective sheet sample prepared by the same method as above using inks 1 to 5, a design evaluation test is performed by visually observing the surface from a position 30 cm away from the surface, and the design is sensually evaluated. evaluated. All the test pieces had a size of 100 mm × 100 mm. Regarding the refractive index of the resin component of the dark color layer made of the test near-infrared transmissive dark color ink used in each example and the comparative example, the other examples were cured under the same conditions without adding a pigment and a filler. The refractive index of the obtained resin layer was measured in advance with a Carnew precision refractometer (KPR-30) manufactured by Shimadzu Corporation. The refractive index of the resin component of the dark color layer made of the test near-infrared transmissive dark color ink was 1.50.
[Evaluation criteria]
◯: The presence of transparent silica cannot be visually recognized, and the appearance of dark color is maintained.
Δ: The presence of transparent silica is slightly visible, but the appearance is generally dark.
X: The presence of transparent silica is visually recognized, and the appearance of dark color is impaired.

From Table 1, in a solar cell module provided with a dark color layer made of a near-infrared transmissive dark color ink that can contribute to improving the power generation efficiency of the solar cell module, the average particle size is optimized relative to the thickness of the dark color layer. The back surface protective sheet of the present invention in which a dark color layer is formed by a dark color ink containing an appropriate amount of the transparent inorganic filler is considered to be a back surface protective sheet having excellent blocking resistance while maintaining a preferable design property. I understand.

1 Solar cell module 2 Transparent front substrate 3 Front encapsulant layer 4 Solar cell element 5 Back encapsulant layer 6 Backside protective sheet 61 Base material layer 62 Dark color layer 63 Transparent adhesive layer 64 Transparent adhesive layer

Claims (1)

A base material layer and a dark color layer that transmits near infrared rays having a wavelength of 750 nm or more and 1500 nm or less are provided.
The dark color layer contains a resin component, a dark color pigment, and a transparent inorganic filler.
The content of the transparent inorganic filler contained in the dark color layer is 0.5 parts by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the resin component.
A back surface protective sheet for a solar cell in which the average particle size of the transparent inorganic filler is 50% or more and 150% or less with respect to the thickness of the dark color layer.

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