JP2014216345A - Resin sealing sheet for solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a resin sealing sheet for solar cell having excellent stacking properties and capable of preventing the problem of cell deviation.SOLUTION: A resin sealing sheet for solar cell contains at least one kind of resin selected from a group of polyethylene-based resin, polypropylene-based resin, and polybutene-based resin, and has a recess provided in at least one side, in which the percentage V/V×100% of the total volume Vof the recess per unit area and the apparent volume V, i.e., the product of the unit area and the maximum thickness, is 5-80%.

Description

  The present invention relates to a resin encapsulating sheet for solar cells.

  In recent years, awareness of the environment has increased due to global warming phenomena, and new energy systems that do not generate carbon dioxide and other gases that are said to induce warming (hereinafter also referred to as “warming gases”) have attracted attention. ing. For example, an environmentally friendly renewable energy system such as a solar cell power generation system or a wind power generation system does not emit greenhouse gases, and therefore, research and development are actively conducted as a clean energy system. In particular, from the viewpoint of safety and ease of handling, the solar cell power generation system is attracting attention not only as a household energy source but also as an industrial energy source. In Japan, where resources are scarce, in each household, installing a solar cell power generation system on the roof to generate electricity, consuming the resulting power as household power, or selling surplus power, In recent years, it has been actively performed. In Europe, mainly in Germany, not only for home use but also for large-scale power generation by arranging solar cells on a vast site. Solar power generation systems are also subject to investment as industrial power. Is also attracting attention.

  There are various power generation methods for solar cells that are attracting attention in this way. As a typical power generation method, as a power generation portion, a single crystal or polycrystalline silicon cell (crystalline silicon cell), an amorphous silicon, or a compound semiconductor (thin film cell) is used. Etc. Solar cells are exposed to wind and rain outdoors for quite a long time. Therefore, for the purpose of protecting the power generation part for a long period of time, it is known that the power generation part is bonded with a glass plate or a back sheet to form a module. By protecting the power generation portion in this way, inflow of moisture from the outside and leakage are prevented, and stable protection of the power generation portion is achieved over a long period of time. In the above module structure, it is necessary to transmit the light source necessary for power generation on the power generation surface side of the power generation portion, so transparent glass or transparent resin is used, and aluminum called a back sheet is used on the non-power generation surface side of the power generation portion. A laminated sheet of barrier coating such as foil, polyvinyl fluoride resin (PVF), polyethylene terephthalate (PET) or silica thereof is used. Here, “modularization” means that the resin encapsulating sheet is melted by sandwiching the power generation part between the resin encapsulating sheet and then covering the outside further with glass or a back sheet to raise the temperature of the resin encapsulating sheet. , It means that everything is integrated and sealed (modularized).

  Such a resin encapsulated sheet includes <1> adhesion to glass, a power generation part and a back sheet, and <2> prevention of flow of the power generation part due to melting of the resin encapsulated sheet in a high temperature state (creep resistance). ), <3> Transparency that does not inhibit sunlight is a required characteristic. Usually, such a resin encapsulated sheet is made of an ethylene-vinyl acetate copolymer (hereinafter also referred to as “EVA”) with a light-proofing agent, an ultraviolet absorber, or a glass for improving adhesion to glass as a measure against ultraviolet deterioration. It can be produced by forming a ring agent or an additive such as an organic peroxide for crosslinking into a film by calendar molding or T-die casting.

  In addition, solar cell modules using single crystal or polycrystalline silicon cells are laminated in the order of glass / resin encapsulated sheet / crystalline silicon cell power generation part / resin encapsulated sheet / back sheet, with the glass surface down. Then, using a dedicated solar cell vacuum laminator, each of the resin encapsulated sheets is melted through a preheating step and a pressing step above the melting temperature of the resin used (in the case of EVA, a temperature condition of 150 ° C.). It can manufacture by bonding a member.

  At this time, the resin of the resin sealing sheet is melted in the first preheating process, and the resin melted in the pressing process and the member in contact with the resin are bonded and vacuum laminated. In these steps, the organic peroxide contained in the resin sealing sheet is decomposed by heat and promotes EVA crosslinking. Furthermore, the coupling agent contained in the resin sealing sheet is covalently bonded to the surface of the member in contact with the resin sealing sheet, thereby further improving the adhesion between the resin sealing sheet and the member. Thereby, the flow of the electric power generation part resulting from melting of the resin sealing sheet in a high temperature state is prevented (creep resistance), and the adhesiveness with the glass, the electric power generation part, and the back sheet is improved. In addition, since the resin-encapsulated sheet is exposed to sunlight for a long time, an additive such as a light-resistant agent is blended from the viewpoint of preventing a decrease in optical characteristics due to deterioration of the resin. As a result, a level of transparency that does not hinder sunlight can be maintained over a long period of time.

  For example, Patent Document 1 discloses a module in which an organic polymer resin encapsulating sheet crosslinked by electron beam irradiation is laminated on an amorphous silicon solar cell. Examples of the resin forming the organic polymer resin encapsulating sheet include ethylene-vinyl acetate copolymer (EVA) and ethylene-methyl acrylate (EMA). These organic polymer resin encapsulating sheets further contain an antioxidant, an ultraviolet absorber, a light stabilizer, and a silane coupling agent. And in patent document 1, it vacuum-laminates at 150 degreeC with an electric power generation part and a back sheet | seat using the resin sealing sheet sheeted by extrusion molding from the slit, and the module is produced. Patent Document 1 discloses that a crosslinking treatment is performed by irradiating an irradiation voltage of 300 kGy with an acceleration voltage of 500 kV from the light receiving surface of the module, or using a resin sealing sheet that has been crosslinked by electron beam irradiation at 180 ° C. It is described that a solar cell module excellent in creep resistance and weather resistance can be provided by producing a module by vacuum lamination.

  Patent Document 2 discloses a solar cell element sealing material made of an ethylene copolymer subjected to electron beam irradiation. As a representative of the ethylene copolymer, a resin selected from the group consisting of an ethylene-vinyl acetate copolymer (EVA), an ethylene-unsaturated carboxylic acid ester copolymer, and an ethylene-unsaturated carboxylic acid copolymer is used. Patent Document 2 discloses a solar cell element sealing material having creep resistance that does not flow or deform when the cross-linking gelation rate is 65% or higher. It is stated that it can be provided.

  Patent Document 3 discloses a technique related to a resin encapsulating sheet obtained by irradiating ionizing radiation cross-linked resin with ionizing radiation.

  Patent Document 4 discloses a technique related to a resin-encapsulated sheet having a specific gel fraction and a heat shrinkage rate at 60 ° C. in a specific range.

Patent Document 5 discloses a film obtained by forming an ethylene-vinyl acetate copolymer resin. The film is provided with recesses by embossing, and the total volume V of the recesses per unit area of the film. A technique relating to a film in which the percentage of _H and the apparent volume VA of the film obtained by multiplying the unit area by the maximum thickness is in a specific range is disclosed.

JP-A-6-334207 JP 2001-119047 A JP 2009-249556 A JP 2010-226054 A Japanese Patent No. 3473605

  For example, the above patent document discloses a resin-encapsulated sheet in which heat resistance is provided by crosslinking a resin by irradiating an ethylene vinyl copolymer represented by an ethylene-vinyl acetate copolymer (EVA) with an electron beam. Has been. By applying such a resin encapsulating sheet to a solar cell module, the resin encapsulating sheet is prevented from flowing when the solar cell module exposed to the summer sun is in a high temperature state (creep resistance). )be able to.

  However, since the resin-encapsulated sheet of the prior art has a high gel fraction in the resin, it was formed on the solar cell glass itself in order to improve the light condensing characteristics and adhesion when previously crosslinked using an electron beam. In some cases, the unevenness and the unevenness resulting from the thickness of the wiring or the power generation cell cannot be reliably sealed without a gap. In this case, since the air remaining in the gap repeatedly expands and contracts due to a temperature change such as a temperature change, the resin sealing sheet may be peeled off. In addition, moisture or the like may flow into the gap and may invade the power generation portion, increasing the risk of leakage. Furthermore, in a resin-encapsulated sheet that has been previously cross-linked using an electron beam, the rate of relaxation of stress is slowed by cross-linking, so it may be difficult to reduce thermal shrinkage by heat fixation or the like.

  In particular, in the example described in Patent Document 1, since the electron beam irradiation processing of the resin sealing sheet is performed from the light receiving surface side under the conditions of 300 to 500 kV and 300 kGy, the power generation portion can reach the back surface of the crystalline silicon cell. Therefore, a place where the resin sealing sheet is not cross-linked is formed. As a result, the gel fraction of the resin sealing sheet in the module is partially non-uniform. Therefore, there is a case where it is impossible to stably hold the crystalline silicon cell in a high temperature environment, and there remains a problem that an important power generation part flows. In addition, when using a resin-encapsulated sheet that has been subjected to electron beam irradiation treatment under such irradiation conditions before vacuum lamination, unevenness produced in the solar cell glass itself, or unevenness resulting from the thickness of the wiring or power generation cell Cannot be reliably sealed with a resin sealing sheet without a gap. As a result, it is necessary to change the lamination conditions when manufacturing the solar cell module. In many cases, it is necessary to increase the laminating temperature by about 30 ° C., which may cause problems such as excessive damage to the power generation portion and a decrease in power generation efficiency. Moreover, although only the technique which press-molds about the manufacturing method of a sheet | seat is disclosed by the Example described in patent document 1, since productivity is very low in this method, it cannot apply to commercial production.

  Patent Document 2 describes that a resin-sealed sheet having a higher gelation rate is superior in heat resistance. However, when the resin-sealed sheet having a high gelation rate is preliminarily electron-crosslinked, as in Patent Document 1, the unevenness formed in the solar cell glass itself or the unevenness resulting from the thickness of the wiring or power generation cell is resin-sealed. The sheet cannot be reliably sealed without a gap. As a result, it is necessary to change the lamination conditions when manufacturing the solar cell module. In many cases, it is necessary to increase the laminating temperature by about 30 ° C., which may cause excessive damage to the power generation portion and decrease the power generation efficiency. Moreover, in patent document 2, there is no indication except having extruded from the slit about the manufacturing method of the resin sealing sheet.

  Patent Document 3 discloses a method for producing a resin-encapsulated sheet. For extrusion, a T-die method, a circular die (annular die) method, or the like can be used. In the case of multiple layers, a circular die (annular die) method is preferable. In the examples, an annular die (circular die) method is used.

  Patent Document 4 discloses a resin-encapsulated sheet having a heat shrinkage rate of 60 ° C. in a specific range, and all examples in Patent Document 4 use an annular die (circular die). However, in patent document 4, the temperature (usually higher than 60 degreeC) of the resin sealing sheet in the preheating process of the lamination process at the time of manufacturing a solar cell module, and melting | fusing point (higher than 60 degreeC) of resin which is a sheet raw material ) The thermal shrinkage rate at higher temperatures is not examined. As a resin encapsulating sheet for use in a solar cell, development of a resin encapsulating sheet having a low thermal shrinkage at a temperature higher than the melting point of the resin as a sheet material, for example, 90 ° C., is desired.

  In Patent Document 5, it is possible to effectively prevent damage to cells and poor deaeration at the time of sealing due to the sealing film being pressed against the solar cell in the sealing step at the time of solar cell production, and sealing. Although the technology that can prevent the resin of the film from protruding and that can produce a high-quality solar cell with a high yield is disclosed, in the process of stacking the members in the modularization process, the resin sealing is particularly important. Since the slip between the stop sheet and the solar battery cell is poor, it takes time to position the members when stacking, and development of a resin-encapsulated sheet that facilitates positioning is desired.

  This invention is made | formed in view of the said problem, and it aims at providing the resin sealing sheet for solar cells which is excellent in stackability and can prevent the malfunction of a cell shift.

  As a result of intensive studies to solve the above problems, the present inventors have found that the above problems can be solved if a resin-encapsulated sheet for a solar cell containing a predetermined resin and having a predetermined shape is completed. It came to do.

That is, the present invention is as follows.
[1]
Including at least one resin selected from the group consisting of polyethylene resins, polypropylene resins, polybutene resins,
A recess is provided on at least one side,
The percentage V _H / V _A × 100% of the total volume V _{H of the} recesses per unit area and the apparent volume V _A obtained by multiplying the unit area by the maximum thickness is 5 to 80%.
Resin encapsulating sheet for solar cells.
[2]
The resin-encapsulated sheet for solar cells according to [1] above, wherein the layer containing the resin is subjected to ionizing radiation irradiation treatment and has a gel fraction of 1 to 65% by mass.
[3]
The resin-encapsulated sheet for solar cells according to [1] or [2] above, wherein the thermal shrinkage at 90 ° C. is 15% or less.

  ADVANTAGE OF THE INVENTION According to this invention, the resin sealing sheet for solar cells which is excellent in stackability and can prevent the malfunction of a cell shift can be provided.

  Hereinafter, a mode for carrying out the present invention (hereinafter referred to as “the present embodiment”) will be described in detail. In addition, this invention is not limited to the following embodiment, It can implement by changing variously within the range of the summary.

[Resin encapsulating sheet for solar cells]
The solar cell resin encapsulating sheet (hereinafter also simply referred to as “resin encapsulating sheet”) according to this embodiment is at least one resin selected from the group consisting of polyethylene resins, polypropylene resins, and polybutene resins. The ratio of the total volume V _{H of the} recesses per unit area to the apparent volume V _A obtained by multiplying the unit area by the maximum thickness V _H / V _A × 100% Is 5 to 80%. By using such a resin-sealed sheet, the thermal shrinkage rate at a higher temperature (for example, 90 ° C.) is lowered while maintaining the gap filling property in the modularization process and the creep resistance after modularization. Therefore, problems such as cell shift in the modularization process can be prevented, and the positioning of the members in the process of stacking the members in the modularization process can be facilitated.

  The resin-encapsulated sheet according to the present embodiment contains at least one kind of resin selected from the group consisting of polyethylene-based resins, polypropylene-based resins, and polybutene-based resins. Easy positioning when stacked. Moreover, at the time of the heat processing of the sealing process at the time of manufacture of a solar cell, the wide passage of air is ensured by the recessed part provided in the resin sealing sheet, and deaeration property improves. For this reason, deaeration failure is prevented and the sealing time can be shortened. In addition, during the heat processing in the sealing step when manufacturing the solar cell, the resin that has flowed flows into the recesses, so that the resin is prevented from protruding.

<Sealing method>
The resin-encapsulated sheet according to the present embodiment is a resin-encapsulated sheet used for encapsulating solar cells. For example, when producing a solar cell module composed of glass, a power generation portion, and a back sheet, each configuration Used for sealing members. Although it does not specifically limit as a sealing method, For example, the method of softening a resin sealing sheet and sticking the softened resin sealing sheet to a to-be-sealed material, and solidifying resin is mentioned. When long-term durability is required, it is preferable that the resin-encapsulated sheet is closely adhered between the material to be encapsulated and the material to be encapsulated in order to stably fix it. In such a case, a method that excludes air, such as a vacuum laminating method, is usually used, but the method is not limited to this.

  Here, “to soften the resin sealing sheet” means to give energy such as heat to the resin sealing sheet to make the resin in the resin sealing sheet softened. Although it does not specifically limit as energy, Since heating is simple, it is preferable. Also, how to give energy such as heat to the resin is a method of heating directly with heating wire, an indirect heating method such as radiant heat, a method of generating heat by causing molecular motion of the resin itself by vibrating the molecular chain of the resin Any method may be used.

<resin>
The resin sealing sheet according to the present embodiment includes at least one resin selected from the group consisting of a polyethylene resin, a polypropylene resin, and a polybutene resin (hereinafter also referred to as “resin used in the present embodiment”). . When the resin encapsulating sheet according to the present embodiment has a single layer structure, the layer may be composed of the above-mentioned single resin, the two or more kinds of resins described above, or the resin used in the present embodiment and others. You may be comprised from resin obtained by mixing this resin. Moreover, when the resin sealing sheet which concerns on this embodiment is a multilayer structure, each layer may be comprised from said single resin, The resin used for said 2 or more types or this embodiment, and You may be comprised from resin obtained by mixing with other resin.

(Polyethylene resin)
Although it does not specifically limit as said polyethylene-type resin, For example, polyethylene, an ethylene-alpha-olefin copolymer, etc. are mentioned. Polyethylene resins are preferred because they are easily crosslinked when irradiated with ionizing radiation.

  The polyethylene is not particularly limited, and for example, low density polyethylene (hereinafter also referred to as “LDPE”), linear low density polyethylene (hereinafter also referred to as “LLDPE”), linear ultra-low density polyethylene (hereinafter referred to as “LDPE”). , "VLDPE" or "ULDPE").

  Although it does not specifically limit as said ethylene-alpha-olefin copolymer, For example, it is a copolymer which consists of ethylene and at least 1 sort (s) chosen from the group which consists of C3-C20 alpha olefins. Preferably, it is a copolymer composed of ethylene and at least one selected from the group consisting of α-olefins having 3 to 12 carbon atoms. The α-olefin is not particularly limited, and examples thereof include 1-pentene, 1-hexene, 1-octene, 4-methyl-1-pentene, 3-methyl-1-pentene, 1-decene and 1-dodecene. 1-tetradecene, 1-hexadecene, 1-octadecene, 1-eicosane and the like. The α-olefin may be used alone or in combination of two or more. Moreover, it is preferable that the ratio (based on preparation monomer) of the alpha olefin in all the monomers which comprise a copolymer is 6-30 mass%. Further, the ethylene-α-olefin copolymer is preferably a soft copolymer, the crystallinity by X-ray method is preferably 30% or less, and more preferably 25% or less. More preferably, it is 20% or less. When the degree of crystallinity is in the above range, it tends to be softened more easily.

  The ethylene-α-olefin copolymer as described above is preferably a copolymer of ethylene and at least one comonomer selected from the group consisting of propylene comonomer, butene comonomer, hexene comonomer, and octene comonomer. Such a copolymer is generally easily available and can be suitably used.

  Although the said polyethylene-type resin is not specifically limited, For example, it can superpose | polymerize using well-known catalysts, such as a single site type catalyst and a multisite type catalyst, It is preferable to superpose | polymerize using a single site type catalyst.

The polyethylene resin preferably has a density of 0.860 to 0.920 g / cm ³ , more preferably 0.870 to 0.915 g / cm ³ , and 0.870 to 0.910 g / cm ^3. More preferably, it is cm ³ . When the density is 0.920 g / cm ³ or less, the cushioning property becomes better and the transparency tends to be better. When a high-density polyethylene-based resin is used, the transparency can be improved by adding a low-density polyethylene-based resin at a ratio of about 30% by mass, for example.

  The melt flow rate (hereinafter also referred to as “MFR”) (190 ° C., 2.16 kg) of the polyethylene-based resin is preferably 0.5 g / 10 min to 30 g / 10 min, and preferably 0.8 g / 10 min to 30 g. / 10 min is more preferable, and 1.0 g / 10 min to 25 g / 10 min is further more preferable. When MFR is in the above range, the processability of the resin-encapsulated sheet tends to be more excellent. In this embodiment, MFR can be measured by the method described in the Examples. Moreover, it is preferable that Vicat softening point is 40-90 degreeC, It is more preferable that it is 43-75 degreeC, It is further more preferable that it is 45-60 degreeC. When the Vicat softening point is in the above range, the processability of the resin-encapsulated sheet tends to be superior. In this embodiment, the Vicat softening point can be measured according to JIS K 7206-1982.

  As said polyethylene-type resin, the polyethylene-type copolymer which controlled crystal / amorphous structure (morphology) by nano order can also be used.

(Polypropylene resin)
Although it does not specifically limit as said polypropylene resin, For example, a ternary copolymer of a polypropylene, a propylene-alpha-olefin copolymer, a propylene, ethylene, and an alpha olefin etc. are mentioned. When the resin used in the present embodiment contains the polypropylene resin, hardness and heat resistance are further improved.

  The propylene-α-olefin copolymer is not particularly limited. For example, a copolymer composed of propylene and at least one selected from the group consisting of ethylene and an α-olefin having 4 to 20 carbon atoms is preferable. More preferred is a copolymer composed of at least one selected from the group consisting of propylene, ethylene, and an α-olefin having 4 to 8 carbon atoms. Examples of the α-olefin having 4 to 20 carbon atoms include 1-pentene, 1-hexene, 1-octene, 4-methyl-1-pentene, 3-methyl-1-pentene, 1-decene, 1 -Dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, 1-eicosane and the like. These α-olefins may be used alone or in combination of two or more. Moreover, it is preferable that the content rate (charged monomer reference | standard) of ethylene and / or alpha-olefin in all the monomers which comprise the said propylene-alpha-olefin copolymer is 6-30 mass%. Further, the propylene-α-olefin copolymer is preferably a soft copolymer, the crystallinity by X-ray method is preferably 30% or less, and more preferably 25% or less. More preferably, it is 20% or less. When the degree of crystallinity is in the above range, it tends to be softened more easily.

  The propylene-α-olefin copolymer is preferably a copolymer of propylene and at least one comonomer selected from the group consisting of ethylene comonomer, butene comonomer, hexene comonomer, and octene comonomer. Such a copolymer is generally easily available and can be suitably used.

  Although the said polypropylene resin is not specifically limited, For example, it can superpose | polymerize using well-known catalysts, such as a single site type catalyst and a multisite type catalyst, It is preferable to superpose | polymerize using a single site type catalyst.

Also it is preferable that the density of the polypropylene-based resin is 0.860~0.920g / cm ^3, more preferably 0.870~0.915g / cm ^3, 0.870~0.910g / cm ³ is more preferable. When the density is 0.920 g / cm ³ or less, the cushioning property becomes better and the transparency tends to be better.

  The MFR (230 ° C., 2.16 kgf) of the polypropylene resin is preferably 0.3 g / 10 min to 15.0 g / 10 min, more preferably 0.5 g / 10 min to 12 g / 10 min. More preferably, it is 8 g / 10 min to 10 g / 10 min. When MFR is in the above range, the processability of the resin-encapsulated sheet tends to be more excellent.

  As the polypropylene resin, a polypropylene copolymer in which the crystal / amorphous structure (morphology) is controlled in nano order can also be used.

  Examples of the polypropylene resin include copolymers of propylene and α-olefins such as ethylene, butene, hexene, and octene, or ternary compounds of propylene, ethylene and α-olefins such as butene, hexene, and octene. A copolymer etc. can be used conveniently. These copolymers may be in any form such as a block copolymer, a random copolymer, etc., preferably a random copolymer of propylene and ethylene, or a random copolymer of propylene, ethylene and butene. is there.

  The polypropylene resin may be not only a resin polymerized with a catalyst such as a Ziegler-Natta catalyst, but also a resin polymerized with a metallocene catalyst, for example, syndiotactic polypropylene, isotactic polypropylene, etc. it can. Further, the proportion of propylene in all monomers constituting the polypropylene resin (based on charged monomers) is preferably 60 to 80% by mass, more preferably 10 to 30% by mass, and 5 to 20% by mass. More preferably. When the ratio is within the above range, it tends to be more excellent in heat shrinkability.

  As the polypropylene resin, a resin obtained by uniformly finely dispersing a rubber component having a high concentration of 50% by mass or less with respect to the total amount of the polypropylene resin can be used.

(Polybutene resin)
The polybutene-based resin is not particularly limited, and examples thereof include polybutene, a butene-α-olefin copolymer, and a terpolymer of butene and ethylene or polypropylene and α-olefin. Hardness improves more because the resin used for this embodiment contains the said polybutene-type resin.

  The butene-α-olefin copolymer is not particularly limited. For example, a copolymer comprising butene and at least one selected from the group consisting of ethylene or polypropylene and an α-olefin having 4 to 20 carbon atoms. A copolymer comprising at least one selected from the group consisting of butene, ethylene or polypropylene, and an α-olefin having 4 to 8 carbon atoms is more preferable. Examples of the α-olefin having 4 to 20 carbon atoms include 1-pentene, 1-hexene, 1-octene, 4-methyl-1-pentene, 3-methyl-1-pentene, 1-decene, 1 -Dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, 1-eicosane and the like. These α-olefins may be used alone or in combination of two or more.

  Since the polybutene-based resin is particularly excellent in compatibility with the polypropylene-based resin, it is preferably used in combination with the polypropylene-based resin for the purpose of adjusting the hardness and waist of the resin sealing sheet. Although it does not specifically limit as said polybutene-type resin, For example, it is crystalline and is a copolymer which consists of at least 1 sort (s) chosen from the group which consists of butene and ethylene, propylene, and a C5-C8 olefin type compound. In addition, a high molecular weight polybutene resin in which the content of butene in all monomers constituting the polybutene resin is 70 mol% or more can be preferably used.

  The MFR (190 ° C., 2.16 kg) of the polybutene-based resin is preferably 0.1 g / 10 min to 10 g / 10 min. When MFR is in the above range, the processability of the resin-encapsulated sheet tends to be more excellent. Moreover, it is preferable that a Vicat softening point is 40-100 degreeC. When the Vicat softening point is in the above range, cell cracks during lamination when producing a solar cell module tend to be excellent.

(Thermoplastic resin)
When the resin sealing sheet according to the present embodiment has a multilayer structure, the layer containing the resin used in the present embodiment can be used for the surface layer, and the layer containing the resin used in the present embodiment may be used as the inner layer. Any other resin-containing layer may be used. Among these, it is preferable that the resin used in the present embodiment is included in the surface layer from the viewpoint of sealing properties. Further, a single resin layer or a resin layer containing a mixture of resins or a mixture of a resin and an additive may be introduced as a new layer in the inner layer. Furthermore, a new layer may be introduced for the purpose of improving cushioning properties. Examples of such a new layer include a layer containing a thermoplastic resin.

  The thermoplastic resin exhibits rubber elasticity at room temperature and has thermoplasticity, and may be a blend of copolymer rubber and polymer in an arbitrary weight ratio. The copolymer rubber can be present in the thermoplastic resin in a state such as uncrosslinked, partially crosslinked, or entirely crosslinked.

  Such a thermoplastic resin is not particularly limited, and examples thereof include olefin resins, styrene resins, vinyl chloride resins, polyester resins, urethane resins, chlorine resins, ethylene polymer resins, polyamide resins, and the like. Examples thereof include biodegradable resins and plant-derived raw material resins. In the present embodiment, the thermoplastic resin includes a hydrogenated block copolymer resin, a propylene copolymer resin, and an ethylene copolymer resin that have good compatibility with the crystalline polypropylene resin and good transparency. A hydrogenated block copolymer resin and a propylene-based copolymer resin are more preferable.

  Although it does not specifically limit as said hydrogenated block copolymer resin, For example, the block copolymer of vinyl aromatic hydrocarbon and conjugated diene is preferable. Although it does not specifically limit as a vinyl aromatic hydrocarbon, For example, styrene, o-methylstyrene, p-methylstyrene, p-tert-butylstyrene, 1,3-dimethylstyrene, alpha-methylstyrene, vinylnaphthalene, vinyl Anthracene, 1,1-diphenylethylene, N, N-dimethyl-p-aminoethylstyrene, N, N-diethyl-p-aminoethylstyrene and the like can be mentioned. Of these, styrene is preferable. These may be used alone or in combination of two or more.

  Although it does not specifically limit as said conjugated diene, For example, it is a diolefin which has a pair of conjugated double bond, Specifically, 1, 3- butadiene, 2-methyl- 1, 3- butadiene (isoprene) 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene and the like. These may be used alone or in combination of two or more.

  Although it does not specifically limit as said propylene-type copolymer resin, For example, the copolymer obtained from a propylene and ethylene or a C4-C20 alpha olefin is preferable. The content of ethylene or the α-olefin having 4 to 20 carbon atoms is preferably 6 to 30% by mass. Here, the α-olefin having 4 to 20 carbon atoms is not particularly limited, and specifically, 1-butene, 1-pentene, 1-hexene, 1-octene, 4-methyl-1-pentene, Examples include 3-methyl-1-pentene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, 1-eicosane and the like.

  Although the said propylene-type copolymer resin is not specifically limited, For example, what was polymerized using any catalyst, such as a multi-site type catalyst, a single site type catalyst, may be used.

  Furthermore, a propylene-based copolymer in which the crystal / amorphous structure (morphology) of the polymer is controlled in nano order can also be used.

  The ethylene copolymer resin may be a multi-site catalyst, a single-site catalyst, or any other polymer polymerized by any other catalyst. In addition, an ethylene copolymer in which the crystal / amorphous structure (morphology) of the polymer is controlled in the nano order can also be used. In addition to the above resins, there is no problem even if a known resin such as an ionomer is introduced as a single layer or mixed.

<Recess>
The resin sealing sheet according to the present embodiment is provided with a recess on at least one surface, and the resin sealing sheet obtained by multiplying the total volume V _H of the recess per unit area of the resin sealing sheet by the maximum thickness. The percentage V _H / V _A × 100% with respect to the apparent volume V _A is 5 to 80%, preferably 7 to 50%, more preferably 10 to 30%. Moreover, when the percentage V _H / V _A × 100% is within the above range, the stackability tends to be more excellent. The percentage V _H / V _A × 100% tends to increase as the embossing depth of the embossing roll is increased, the sheet thickness is decreased, or the temperature of the sheet in contact with the embossing roll is increased. The embossing roll tends to become smaller by decreasing the embossing depth, increasing the sheet thickness, or lowering the temperature of the sheet in contact with the embossing roll.

The porosity P defined by the above V _H / V _A × 100% can be obtained by calculation as follows. That is, in the resin-encapsulated sheet subjected to embossing, the apparent volume V _A (mm ³ ) of the sheet is the maximum thickness t _max (mm) of the resin-encapsulated sheet and a unit area (for example, 1 m ² = 1000 mm × 1000 mm = 1 × 10 ⁶ mm ² ) and calculated as follows.
V _A (mm ³ ) = t _max × 10 ⁶

On the other hand, the actual volume V ₀ (mm ³ ) of the resin encapsulating sheet of this unit area is the specific gravity ρ (g / mm ³ ) of the resin used in this embodiment and the resin encapsulating sheet per unit area (1 m ² ). It is calculated as follows from the actual weight W (g).
V ₀ (mm ³ ) = W / ρ

The total volume V _H (mm ³ ) of the recesses per unit area of the resin sealing sheet is calculated as follows by subtracting the actual volume V ₀ from the apparent volume _VA of the resin sealing sheet.
V _H (mm ³ ) = V _A −V ₀ = V _A − (W / ρ)

Therefore, the porosity (%) can be obtained as follows.
Porosity P (%) = V _H / V _A × 100
= (V _A- (W / ρ)) / V _A × 100
= 100−W / (ρ × V _A ) × 100
= 100−W / (ρ × t _max × 10 ⁶ ) × 100

  In addition, this porosity (%) can also be calculated | required by the above calculation formulas.

  The resin encapsulating sheet having the recesses imparts an appropriate cushioning property to the resin encapsulating sheet at the time of heat processing in the encapsulating process in the production of the solar cell, thereby preventing the solar cell from being damaged. That is, when a pressing force is locally applied to the resin-encapsulated sheet, the convex portion to which the pressing force is applied is deformed to be crushed, and a large force is locally applied to the solar cell. Is prevented. A wide passage of air is secured by the recess provided in the resin sealing sheet at the time of heat processing in the sealing step when manufacturing the solar cell, and the deaeration performance is improved. For this reason, deaeration failure is prevented and the sealing time can be shortened. At the time of heat processing in the sealing step when manufacturing the solar cell, the resin that has flowed flows into the recesses, thereby preventing the resin from protruding. As a result, high-quality solar cells can be manufactured with high yield.

  In the present embodiment, the depth of the recess is preferably 20 to 95% of the maximum thickness of the resin sealing sheet, more preferably 50 to 95%, and still more preferably 65 to 95%. When the depth of the recess is within the above range, the stackability tends to be more excellent. The “depth of the concave portion” in the present embodiment indicates a height difference D between the topmost portion of the convex portion and the deepest portion of the concave portion of the uneven surface of the resin-encapsulated sheet by embossing.

Further, the maximum thickness “t _max ” of the resin sealing sheet indicates the distance from the top to the back of the convex portion when embossing is performed on one surface of the resin sealing sheet. When both surfaces are embossed, the distance between the tips of the convex portions on both surfaces (the distance in the resin encapsulating sheet thickness direction) is shown.

Embossing may be performed on both surfaces of the resin sealing sheet, or may be performed only on one surface. When embossing is performed only on one side of the resin sealing sheet, the maximum thickness _tmax of the resin sealing sheet is 50 to 2000 μm.

<Additive>
The resin sealing sheet according to the present embodiment includes a coupling agent, an antifogging agent, a plasticizer, an antioxidant, a surfactant, a colorant, a light stabilizer, an ultraviolet absorber, and an adhesive resin as necessary. Further, an antistatic agent, a crystal nucleating agent, a lubricant, an antiblocking agent, an inorganic filler, a crosslinking regulator, and the like may be added. These additives can be added to the molten resin as a solution containing the additive, directly kneaded into the target resin layer, applied after film formation, etc. Any known method can be used as long as it is possible.

(Coupling agent)
A coupling agent may be added to the resin sealing sheet according to the present embodiment for the purpose of ensuring stable adhesiveness. In the resin-encapsulated sheet according to the present embodiment, the content of the coupling agent is preferably 0.01 to 5% by mass, more preferably 0.03, although it depends on the desired degree of adhesion and the type of adherend. It is -4 mass%, More preferably, it is 0.05-3 mass%. As a coupling agent, the substance which provides the favorable adhesiveness to the photovoltaic cell, glass, etc. of the resin used for this embodiment is preferable. Such a coupling agent is not particularly limited, and examples thereof include organic silane compounds, organic silane peroxides, and organic titanate compounds. In addition, the method of adding these coupling agents includes a method of mixing with the resin used in the present embodiment in the extruder, a method of mixing in the extruder hopper and mixing with the resin used in the present embodiment, and a master batch in advance. Any known addition method can be used as long as the effect of the coupling agent can be exerted, such as a method of adding a modified agent. However, in the case of the addition method via an extruder, the content of the coupling agent may be increased or decreased depending on the type of the coupling agent because the original function of the coupling agent may be hindered by heat or pressure in the extruder. Is preferred. The type of coupling agent may be appropriately selected from the viewpoints of transparency and dispersion of the resin used in the present embodiment, corrosiveness to the extruder, and extrusion stability.

  Although it does not specifically limit as said coupling agent, For example, what has an unsaturated group and an epoxy group is mentioned. Such a coupling agent is not particularly limited. Specifically, vinyltrichlorosilane, vinyltris (βmethoxyethoxy) silane, vinyltriethoxysilane, vinyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, N-β (aminoethyl) γ-aminopropyltrimethoxysilane, N-β (aminoethyl) γ- Examples include aminopropylmethyldimethoxysilane, γ-aminopropyltriethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, and γ-chloropropyltrimethoxysilane.

  These coupling agents may be used alone or in combination of two or more.

(Adhesive resin)
For the purpose of ensuring stable adhesion, ethylene-vinyl acetate copolymer, ethylene-aliphatic unsaturated carboxylic acid copolymer, ethylene-aliphatic unsaturated carboxylic acid ester copolymer, ethylene-vinyl acetate copolymer At least one adhesive resin selected from the group consisting of a polymer saponified product, an ethylene-vinyl acetate-acrylic ester copolymer saponified product, and an ethylene copolymer containing glycidyl methacrylate may be added. The content of the adhesive resin is preferably 1% by mass or more and 50% by mass or less, more preferably 2% by mass or more and 40% by mass or less, and further preferably 4% by mass or more and 25% by mass or less. preferable. If it is 1 mass% or more, more stable adhesiveness can be secured. Moreover, if it is 50 mass% or less, it exists in the tendency for the stackability in a modularization process to become more favorable.

  The ethylene-vinyl acetate copolymer refers to a copolymer obtained by copolymerization of an ethylene monomer and vinyl acetate. The ethylene-aliphatic unsaturated carboxylic acid copolymer refers to a copolymer obtained by copolymerization of an ethylene monomer and at least one monomer selected from the group consisting of aliphatic unsaturated carboxylic acids. Furthermore, the ethylene-aliphatic unsaturated carboxylic acid ester copolymer is a copolymer obtained by copolymerization of an ethylene monomer and at least one monomer selected from the group consisting of aliphatic unsaturated carboxylic acid esters. Show.

  The copolymerization can be performed by a known method such as a high pressure method or a melting method. Moreover, a multisite catalyst, a single site catalyst, etc. can be used as a catalyst of a polymerization reaction. Moreover, it does not specifically limit as a bond shape of each monomer in the said copolymer, A random bond and a block bond are mentioned. The copolymer is preferably a copolymer polymerized by random bonding using a high-pressure method. By being such a copolymer, it tends to be more excellent in optical characteristics.

  In the ethylene-vinyl acetate copolymer, the ratio of vinyl acetate in all monomers constituting the copolymer is preferably 10 to 40% by mass from the viewpoint of optical properties, adhesiveness, and flexibility. More preferably, it is -35 mass%, and it is further more preferable that it is 15-30 mass%. Moreover, the value of MFR (190 degreeC, 2.16 kg) measured according to JIS-K-7210 from a viewpoint of the workability of a resin sealing sheet may be 0.3g / 10min-30g / 10min. Preferably, it is 0.5 g / min to 30 g / min, more preferably 0.8 g / min to 25 g / min.

  Although it does not specifically limit as said ethylene-aliphatic unsaturated carboxylic acid copolymer, For example, ethylene-acrylic acid copolymer (henceforth "EAA"), ethylene-methacrylic acid copolymer (henceforth, Also referred to as “EMAA”). The ethylene-aliphatic unsaturated carboxylic acid ester copolymer is not particularly limited, and examples thereof include an ethylene-acrylic acid ester copolymer and an ethylene-methacrylic acid ester copolymer. Here, as acrylic acid ester and methacrylic acid ester, ester of acrylic acid or methacrylic acid and C1-C8 alcohols, such as methanol and ethanol, is used suitably.

  These copolymers may be multi-component copolymers obtained by copolymerizing three or more monomers. The multi-component copolymer is not particularly limited. For example, a copolymer obtained by copolymerizing at least three types of monomers selected from the group consisting of ethylene, aliphatic unsaturated carboxylic acid, and aliphatic unsaturated carboxylic acid ester. A polymer is mentioned.

  In the ethylene-aliphatic unsaturated carboxylic acid copolymer, the proportion of the aliphatic unsaturated carboxylic acid in all monomers constituting the copolymer is preferably 3 to 35% by mass. Further, MFR (190 ° C., 2.16 kg) is preferably 0.3 g / 10 min to 30 g / 10 min, more preferably 0.5 g / 10 min to 30 g / 10 min, and 0.8 g / 10 min to More preferably, it is 25 g / 10 min.

  Although it does not specifically limit as said ethylene-vinyl acetate copolymer saponification thing, For example, the partial saponification thing or complete saponification thing of an ethylene-vinyl acetate copolymer is mentioned. The saponified ethylene-vinyl acetate-acrylic acid ester copolymer is not particularly limited, and examples thereof include a partially saponified product or a completely saponified product of an ethylene-vinyl acetate-acrylic acid ester copolymer.

  The ratio of the hydroxyl group in each saponified product is preferably 0.1% by mass to 15% by mass, more preferably 0.1% by mass to 10% by mass in the resin used in the present embodiment. More preferably, it is 0.1 mass%-7 mass%. When the ratio of the hydroxyl group is 0.1% by mass or more, the adhesiveness tends to be better. Moreover, it exists in the tendency for compatibility to become favorable because it is 15 mass% or less, and it exists in the tendency which can reduce the risk that the resin sealing sheet obtained finally becomes cloudy.

  The ratio of the hydroxyl group is determined based on the olefin polymer resin saponified ethylene-vinyl acetate copolymer or saponified ethylene-vinyl acetate-acrylic ester copolymer, and VA% of these resins (vinyl acetate by NMR measurement). It can be calculated from the copolymerization ratio), the degree of saponification, and the blending ratio in the resin.

  The content of vinyl acetate in the ethylene-vinyl acetate copolymer and the ethylene-vinyl acetate-acrylic acid ester copolymer before saponification is determined from the viewpoint of obtaining good optical properties, adhesiveness, and flexibility. It is preferable that it is 10-40 mass% with respect to the whole coalescence, It is more preferable that it is 13-35 mass%, It is further more preferable that it is 15-30 mass%. The saponification degree of the saponified ethylene-vinyl acetate copolymer and the saponified ethylene-vinyl acetate-acrylic acid ester copolymer is 10 to 70% from the viewpoint of obtaining good transparency and adhesiveness. Is preferably 15 to 65%, more preferably 20 to 60%.

  Examples of the saponification method include a method of saponifying an ethylene-vinyl acetate copolymer, an ethylene-vinyl acetate-acrylic ester copolymer pellet or powder using an alkali catalyst in a lower alcohol such as methanol, and toluene. And a method of dissolving a copolymer in advance using a solvent such as xylene or hexane and then saponifying it using a small amount of alcohol and an alkali catalyst. Moreover, you may graft-polymerize the monomer containing functional groups other than a hydroxyl group to the saponified copolymer.

  Since each saponified product has a hydroxyl group in the side chain, the adhesiveness is improved as compared with the copolymer before saponification. Moreover, transparency and adhesiveness can be controlled by adjusting the amount of hydroxyl groups (degree of saponification).

  The ethylene copolymer containing glycidyl methacrylate refers to an ethylene copolymer and an ethylene terpolymer with glycidyl methacrylate having an epoxy group as a reaction site. The ethylene copolymer containing such glycidyl methacrylate is not particularly limited. For example, ethylene-glycidyl methacrylate copolymer, ethylene-glycidyl methacrylate-vinyl acetate copolymer, ethylene-glycidyl methacrylate-methyl acrylate copolymer Examples include coalescence. Since the above compounds have high reactivity of glycidyl methacrylate, they can exhibit stable adhesion, and have a low glass transition temperature and tend to have good flexibility.

  In order to increase the stability, the resin-encapsulated sheet according to this embodiment preferably contains at least one additive selected from the group consisting of an antioxidant, an ultraviolet absorber, and a light stabilizer.

(Antioxidant)
It is preferable to add an antioxidant to the resin-encapsulated sheet according to this embodiment in order to impart stability at high temperatures. In the resin sealing sheet according to the present embodiment, the content of the antioxidant is preferably 0.1 to 1 part by mass with respect to 100 parts by mass of the resin used in the present embodiment. The chemical structure of the antioxidant is preferably a monophenol compound, a bisphenol compound, a high molecular phenol compound, a sulfur compound, or a phosphoric acid compound.

  Although it does not specifically limit as a monophenol type antioxidant, For example, 2, 6- di-tert- butyl-p-cresol, butylated hydroxyanisole, 2, 6-di-tert- butyl-4-ethyl phenol N-octadecyl- (4-hydroxy-3,5-ditertiarybutylphenyl) propionate.

  The bisphenol-based antioxidant is not particularly limited, and examples thereof include 2,2′-methylene-bis- (4-methyl-6-tert-butylphenol), 2,2′-methylene-bis- (4-ethyl- 6-tert-butylphenol), 4,4′-thiobis- (3-methyl-6-tert-butylphenol), 4,4′-butylidene-bis- (3-methyl-6-tert-butylphenol), 3,9 -Bis [{1,1-dimethyl-2- {β- (3-tert-butyl-4-hydroxy-5-methylphenyl) propionyloxy} ethyl} 2,4,8,10-tetraoxaspiro] 5 5-Undecane is fisted.

  The polymeric phenolic antioxidant is not particularly limited, and examples thereof include 1,1,3-tris- (2-methyl-4-hydroxy-5-tert-butylphenyl) butane and 1,3,5-trimethyl. -2,4,6-tris (3,5-di-tert-butyl-4-hydroxybenzyl) benzene, tetrakis- {methylene-3- (3 ', 5'-di-tert-butyl-4'-hydro Kissphenyl) propionate} methane, bis {(3,3′-bis-4′-hydroxy-3′-tert-butylphenyl) butyric acid} glycol ester, 1,3,5-tris (3 ′, 5 '-Di-tert-butyl-4'-hydroxybenzyl) -s-triazine-2,4,6- (1H, 3H, 5H) trione, triphenol (vitamin E) That.

  Although it does not specifically limit as a sulfur type antioxidant, For example, a dilauryl thiodipropionate, a dimyristyl thiodipropionate, a distearyl thiopropionate is mentioned.

  Although it does not specifically limit as a phosphoric acid type antioxidant, For example, a triphenyl phosphite, a diphenylisodecyl phosphite, a phenyl diisodecyl phosphite, 4,4'- butylidene-bis- (3-methyl-6-tert-butyl) Phenyl-di-tridecyl) phosphite, cyclic neopentanetetraylbis (octadecylphosphite), tris (mono and / or di) phenyl phosphite, diisodecylpentaerythritol diphosphite, 9,10-dihydro-9-oxa -10-phosphaphenanthrene-10-oxide, 10- (3,5-di-tert-butyl-4-hydroxybenzyl) -9,10-dihydro-9-oxa-10-phosphaphenanthrene-10 -Oxide, 10-decyloxy-9,10-di Dro-9-oxa-10-phosphaphenanthrene, cyclic neopentanetetraylbis (2,4-di-tert-butylphenyl) phosphite, cyclic neopentanetetraylbis (2,6-di-) tert-methylphenyl) phosphite, 2,2-methylenebis (4,6-tert-butylphenyl) octyl phosphite.

  These antioxidants may be used alone or in combination of two or more.

(UV absorber)
Furthermore, the resin-encapsulated sheet according to the present embodiment is for suppressing the light deterioration of the resin used in the present embodiment and improving the weather resistance, or for protecting the lower layer of the layer containing the resin used in the present embodiment. It is preferable to further add an ultraviolet absorber. In the resin sealing sheet according to the present embodiment, the content of the ultraviolet absorber is preferably 0.1 to 0.5 parts by mass with respect to 100 parts by mass of the resin used in the present embodiment. As the ultraviolet absorber, a known compound is used. The chemical structure of the ultraviolet absorber is not particularly limited, and examples thereof include salicylic acid compounds, benzophenone compounds, benzotriazole compounds, and cyanoacrylate compounds.

  Although it does not specifically limit as a salicylic-acid type ultraviolet absorber, For example, a phenyl salicylate, p-tert- butylphenyl salicylate, p-octylphenyl salicylate is mentioned.

  Although it does not specifically limit as a benzophenone series ultraviolet absorber, For example, 2, 4- dihydroxy benzophenone, 2-hydroxy-4- methoxy benzophenone, 2-hydroxy-4- octoxy benzophenone, 2-hydroxy-4- dodecyloxy benzophenone 2,2′-dihydroxy-4-methoxybenzophenone, 2,2′-dihydroxy-4,4′-dimethoxybenzophenone, 2-hydroxy-4-methoxy-5-sulfobenzophenone, bis (2-methoxy-4-hydroxy) -5-benzophenone) methane.

  Although it does not specifically limit as a benzotriazole type ultraviolet absorber, For example, 2- (2'-hydroxy-5'-methylphenyl) benzotriazole, 2- (2'-hydroxy-5'-tert-butylphenyl) benzo Triazole, 2- (2′-hydroxy-3 ′, 5′-di-tert-butylphenyl) benzotriazole, 2- (2′-hydroxy-3′-tert-butyl-5-methylphenyl) -5-chloro Benzotriazole, 2- (2′-hydroxy-3 ′, 5′-di-tert-butylphenyl) -5-chlorobenzotriazole, 2- (2′-hydroxy-3 ′, 5′-di-tert-amyl) Phenyl) benzotriazole, 2- {2′-hydroxy-3 ′-(3 ″, 4 ″, 5 ″, 6 ″ -tetrahydrophthalimidomethyl ) -5'-methylphenyl} benzotriazole, 2,2-methylenebis {4- (1,1,3,3-tetramethylbutyl) -6- (2H-benzotriazol-2-yl) phenol}. .

  Although it does not specifically limit as a cyanoacrylate type ultraviolet absorber, For example, 2-ethylhexyl-2-cyano-3,3'-diphenylacrylate, ethyl-2-cyano-3,3'-diphenylacrylate, etc. are mentioned.

  The said ultraviolet absorber may be used individually by 1 type, or may use 2 or more types together.

(Light stabilizer)
A light stabilizer such as a hindered amine light stabilizer can be added to the resin-encapsulated sheet according to the present embodiment as an additive capable of imparting weather resistance in addition to the ultraviolet absorber. Light stabilizers, such as hindered amine light stabilizers, do not absorb ultraviolet rays like ultraviolet absorbers, but show a significant synergistic effect when used in combination with ultraviolet absorbers. In the resin sealing sheet according to the present embodiment, the content of the light stabilizer is preferably 0.1 to 0.3 parts by mass with respect to 100 parts by mass of the resin used in the present embodiment. A hindered amine light stabilizer is preferable from the viewpoint of ensuring transparency in the resin-encapsulated sheet according to the present embodiment and preventing coloring.

  Although it does not specifically limit as a hindered amine type light stabilizer, For example, succinic acid dimethyl-1- (2-hydroxyethyl) -4-hydroxy-2,2,6,6-tetramethyl piperidine polycondensate, poly [{ 6- (1,1,3,3-tetramethylbutyl) amino-1,3,5-triazine-2,4-diyl} {(2,2,6,6-tetramethyl-4-piperidyl) imino} Hexamethylene {{2,2,6,6-tetramethyl-4-piperidyl) imino}], N, N′-bis (3-aminopropyl) ethylenediamine-2,4-bis [N-butyl-N- ( 1,2,2,6,6-pentamethyl-4-piperidyl) amino] -6-chloro-1,3,5-triazine condensate, bis (2,2,6,6-tetramethyl-4-piperidyl) Separate, 2- ( , 5-Di-tert-4-hydroxybenzyl) -2-n-butylmalonate bis (1,2,2,6,6-pentamethyl-4-piperidyl), bis (2,2,6,6-tetra Methyl-4-piperidinyl) sebacate and the like.

  In consideration of the usage environment of the solar cell module, it is preferable to use a low-volatile ultraviolet absorber, a light stabilizer and a thermal antioxidant.

  When the resin-encapsulated sheet according to the present embodiment has a multilayer structure, the above-described additives such as the ultraviolet absorber, the antioxidant, and the light stabilizer are not limited to the layer containing the resin used in the present embodiment. It may also be added to the resin layer. In this case, in the resin sealing sheet according to the present embodiment, the content of the additive is preferably 0 to 10% by mass, more preferably 0 to 5% by mass with respect to the resin constituting the other resin layer. is there. When the resin constituting the other resin layer is an ethylene-based resin, a resin having a silanol group can be masterbatched and mixed to further impart adhesiveness.

<Bridge>
“Crosslinking” in the present embodiment is to crosslink the polymer constituting the sheet. The crosslinking method is not particularly limited as long as it is a known method, and examples thereof include a crosslinking treatment with an organic peroxide and a crosslinking treatment by irradiation with ionizing radiation (electron beam, γ ray, ultraviolet ray, etc.).

(Crosslinking treatment with organic peroxide)
The crosslinking treatment with the organic peroxide can be carried out, for example, by heating after blending or impregnating the organic peroxide with the resin layer used for the sealing resin sheet or the sealing resin sheet. Although it does not specifically limit as an organic peroxide used here, For example, the organic peroxide whose half life in 100-130 degreeC is less than 1 hour is mentioned. Such an organic peroxide includes 1,1-bis (t-butylperoxy) 3,3,5-trimethylcyclohexane, 1,1-bis (t- Butylperoxy) cyclohexane, n-butyl-4,4-bis (t-butylperoxy) valerate, 2,2-bis (t-butylperoxy) butane, and the like. The encapsulating resin sheet using these organic oxides has a relatively short cross-linking time and can greatly shorten the curing process. These organic peroxides are preferably used in an amount of 10% by mass or less, and in an amount of 5% by mass or less, based on the resin layer used for the sealing resin sheet or the sealing resin sheet. Is more preferable.

(Crosslinking treatment by ionizing radiation irradiation)
In this embodiment, it is preferable to irradiate the resin encapsulating sheet with ionizing radiation such as α rays, β rays, γ rays, neutron rays, and electron beams to crosslink the resin constituting the resin encapsulating sheet. The resin encapsulating sheet according to this embodiment is irradiated with ionizing radiation such as α-rays, β-rays, γ-rays, neutron beams, electron beams, etc., and crosslinked on the resin used in this embodiment. It can bridge | crosslink, without leaving unreacted components, such as an organic acid and a peroxide by elimination | elimination of a chain | strand part, in resin. Thereby, the bad influence to the photovoltaic cell, electroconductive functional layer, or wiring by an unreacted component can be prevented.

  The accelerating voltage of ionizing radiation such as an electron beam may be appropriately selected depending on the thickness of the resin sealing sheet to be subjected to crosslinking treatment. For example, when the resin sealing sheet has a thickness of 500 μm, the entire layer is subjected to crosslinking treatment. In order to apply, an acceleration voltage of 300 kV or more is preferable.

  The irradiation dose of ionizing radiation such as an electron beam is preferably 3 to 500 kGy. Where the irradiation dose of ionizing radiation is within the above range, a uniform cross-linked resin encapsulated sheet is obtained, and the gel fraction of the resin encapsulated sheet does not become too large, with or without solar cells. There is a tendency that the performance of filling the step is improved.

  The accelerating voltage and irradiation dose of ionizing radiation may be appropriately changed in order to achieve a desired gel fraction and gel distribution. The degree of crosslinking generated by the acceleration voltage of ionizing radiation and the irradiation dose is indicated by the gel fraction. The gel fraction of the resin sealing sheet according to the present embodiment that has been subjected to ionizing radiation irradiation treatment is preferably 1 to 65% by mass, more preferably 2 to 60% by mass, and even more preferably 3 to 57% by mass. is there. Because the gel fraction is in the above range, when the members are stacked when assembling the solar cell, the embossed shape of the resin encapsulating sheet is excessively deformed to increase the contact area, thereby increasing the friction between the members. Therefore, it is possible to prevent the workability from deteriorating and to improve the stackability. In this embodiment, a gel fraction can be calculated | required by extracting the resin sealing sheet for 12 hours in boiling p-xylene, and calculating the ratio of an insoluble part. Examples of a method for obtaining a resin-sealed sheet having a gel fraction in the above range include a method of appropriately adjusting the acceleration voltage and irradiation dose of ionizing radiation. In addition, even with the same irradiation dose, a resin-encapsulated sheet having a gel fraction in the above range even when the difference in crosslinking depending on the type of resin or the difference in crosslinking due to crosslinking promotion or suppression by a transfer agent is used. Can be obtained.

  As a method for obtaining a resin encapsulating sheet having a gel fraction in the above range, a method for utilizing the difference in the degree of crosslinking depending on the type of resin and the difference in the degree of crosslinking due to the promotion of crosslinking and the suppression of crosslinking due to additives will be described in detail below. For example, a resin having an ethylene monomer and a polar group such as vinyl acetate, aliphatic unsaturated carboxylic acid or aliphatic unsaturated carboxylic acid ester is disposed on the surface layer of the resin sealing sheet, and linear low density polyethylene (LLDPE) is obtained. ) When the linear ultra-low density polyethylene (VLDPE, ULDPE) resin is arranged in the inner layer, the gel fraction of the surface layer is high even if the accelerating voltage is sufficient to permeate the entire layer, and the gel fraction of the inner layer is Can be lowered. Furthermore, by adjusting the accelerating voltage, the resin layer containing the linear low density density polyethylene (LLDPE) and the linear ultra low density polyethylene (VLDPE, ULDPE) in the inner layer is constructed as an uncrosslinked layer that does not crosslink. Crosslinking processing by irradiation can also be performed. Further, when a polypropylene resin is disposed as the inner layer, the polypropylene resin is not crosslinked by an electron beam or the like, and therefore an uncrosslinked layer can be constructed.

  It is preferable that the resin sealing sheet according to the present embodiment does not contain an organic peroxide that induces a crosslinking reaction. By not containing the organic peroxide, there is no risk of decomposition of the organic peroxide at the distribution stage of the resin-encapsulated sheet, and the temperature conditions during sheet molding can be set in a wide range. In addition, the resin-encapsulated sheet containing no organic peroxide is an organic peroxide that induces a crosslinking reaction while maintaining transparency, adhesiveness, and creep resistance, and other members such as solar cells by decomposition thereof. This eliminates the negative effects on the product, speeds up the process by eliminating the cross-linking process, which was difficult in the past, and reliably seals uneven surfaces such as glass for solar cells, wiring, and the thickness of power generation cells with a resin sealing sheet. be able to.

[Characteristics of resin sealing sheet]
In the resin-encapsulated sheet according to this embodiment, the thermal shrinkage at 90 ° C. is preferably 15% or less, more preferably 10% or less, and further preferably 7% or less. The lower limit of the heat shrinkage rate is not particularly limited, and it is preferably as low as possible, more preferably 0%. When the thermal contraction rate is within the above range, the cell displacement tends to be more excellent. Here, “90 ° C.” is a temperature approximately higher than the melting point of the resin used in this embodiment, which is a raw material of the sealing sheet, and is also a temperature at the time of remaining heat in the laminating process. This is a very effective temperature for evaluating the characteristics of the sheet.

  In the resin-encapsulated sheet according to this embodiment, the thermal shrinkage at 60 ° C. is preferably 5% or less, more preferably 4% or less, and further preferably 3% or less. When the thermal contraction rate is within the above range, the cell shift at the time of lamination when producing a solar cell module tends to be excellent. The lower limit of the heat shrinkage rate is not particularly limited, and it is preferably as low as possible, more preferably 0%. Here, “60 ° C.” is a temperature approximately lower than the melting point of the resin used in the present embodiment.

  In the present embodiment, the thermal shrinkage rate can be measured by the method described in Examples described later. Moreover, the resin sealing sheet whose heat shrinkage rate in 90 degreeC is in the said range can be obtained with the below-mentioned manufacturing method, for example.

  Next, the optical characteristic of the resin sealing sheet according to the present embodiment will be described. The haze of the resin-encapsulated sheet according to the present embodiment is a value measured using an optical measuring machine. Specifically, the haze is a value measured by a method described in Examples described later. The haze is preferably 10.0% or less, more preferably 9.5% or less, and still more preferably 9.0% or less. The lower limit of the haze is not particularly limited and is preferably as low as possible, and more preferably 0%. When the haze is 10.0% or less, there is a tendency that the power generation efficiency of the solar cell tends to be higher, and a sense of security can be obtained because the packaged item can be visually confirmed.

  Moreover, 85% or more of the total light transmittance of the resin sealing sheet which concerns on this embodiment is preferable, More preferably, it is 87% or more, More preferably, it is 88% or more. The lower limit of the total light transmittance is not particularly limited and is preferably as low as possible, more preferably 0%. When the total light transmittance is within the above range, the power generation efficiency of the solar cell tends to be higher. The total light transmittance is a value measured by the method described in Examples described later.

  As for the thickness of the resin sealing sheet which concerns on this embodiment, 50-1500 micrometers is preferable, More preferably, it is 100-1000 micrometers, More preferably, it is 150-800 micrometers. When the thickness of the resin sealing sheet according to the present embodiment is within the above range, the cushioning property of the resin sealing sheet is improved, the workability is improved, the productivity of the solar cell module is improved, and the encapsulation is performed. There is a tendency that the adhesion to the stationary object is improved.

[Method for producing resin-encapsulated sheet]
Next, the manufacturing method of the resin sealing sheet which concerns on this embodiment is described. Although it does not specifically limit as a manufacturing method of the resin sealing sheet which concerns on this embodiment, For example, the method of melt-extruding raw material resin, such as resin used for this embodiment, in a sheet form with an extruder is mentioned.

In the manufacturing method of the resin sealing sheet according to the present embodiment, it is preferable to control the ratio of the extrusion rate of the raw material resin and the winding speed of the resin sealing sheet to a range satisfying the following formula.
1.00 <sheet winding speed / resin extrusion speed ≦ 1.5

In the present embodiment, the winding speed (m / min) of the resin-encapsulated sheet is represented by the length that the sheet is wound per unit time, and the resin extrusion speed is the amount of resin discharged from the die ( kg / min) is divided by the resin density (kg / m ³ ), and the obtained value is divided by the die opening area (m ² ). Since the ratio of the resin extrusion speed and the sheet winding speed is within the above range, it is not necessary to apply a tension when forming the resin-encapsulated sheet, and the orientation of the sheet in the MD direction is increased. Therefore, the thermal contraction rate of the obtained sheet can be lowered, and the thermal contraction rate at 90 ° C. can be controlled to 15% or less.

  In this embodiment, although the resin sealing sheet molding temperature can be set as appropriate, 90 to 170 ° C. is preferable from the viewpoint of the heat shrinkage rate of the obtained resin sealing sheet. When the raw material resin does not contain an organic peroxide, the sheet molding temperature can be increased, which is preferable.

  It is preferable that the manufacturing method of the resin sealing sheet which concerns on this embodiment includes the process of melt | dissolving raw material resin with an extruder, coextruding from a die | dye, and rapidly solidifying it, for example, and obtaining a raw material. At this time, the extrusion can use a T-die method, a circular die (annular die) method, or the like. Of these, the T-die method is preferable.

  The method for producing a resin-sealed processing stop sheet according to this embodiment may include a step of embossing the surface of the resin sealing sheet using the raw material obtained as described above. In the case of double-sided embossing, the surface of the resin-encapsulated sheet can be embossed by passing between two heated embossing rolls, and in the case of single-sided embossing, only one side is passed between heated and embossed rolls. .

  When the resin sealing sheet has a multilayer structure, a multilayer T die method or a multilayer circular die (annular die) method may be used, and a multilayer structure may be formed by a known laminating method, but the multilayer T die method is preferable. .

  The manufacturing method of the resin sealing sheet which concerns on this embodiment may include the post-processing process. Examples of the post-treatment include corona treatment and plasma treatment, and lamination with other types of resin sealing sheets.

  Conventionally, with resin-encapsulated sheets that have been previously cross-linked using an electron beam, the thermal shrinkage of the resin-encapsulated sheet can be reduced to some extent due to cross-linking, but the thermal shrinkage that remains after cross-linking is relaxed due to cross-linking. Since the speed was slow, it was difficult to further reduce thermal shrinkage by heat fixation or the like. However, the resin encapsulating sheet according to the present embodiment is manufactured while controlling the orientation by the winding speed and the molding temperature while reducing the thermal shrinkage by the above-described method, so that the orientation of the resin encapsulating sheet in the MD direction is adjusted. It can be suppressed and further heat shrinkage can be reduced. As a result, problems such as cell shift in the lamination process in the module manufacturing process can be eliminated and the production efficiency of the solar cell module can be improved.

  When the resin-encapsulated sheet according to the present embodiment does not contain an organic peroxide, the resin-encapsulated sheet is used as a resin-encapsulated sheet constituting a module of a solar cell. In addition, while maintaining the creep resistance, there is a tendency that adverse effects on organic peroxides that induce a crosslinking reaction and other members such as solar cells due to decomposition thereof can be eliminated. When the resin-encapsulated sheet according to the present embodiment is previously subjected to crosslinking treatment by irradiating with ionizing radiation, the manufacturing process of the solar cell module is accelerated by eliminating the crosslinking process, which has been difficult in the past. Unevenness such as the thickness of glass, wiring, and power generation cells can be reliably sealed with a resin sealing sheet, and there is a tendency to have recyclability that enables separation of glass and silicon cells when discarded. .

  Hereinafter, although this embodiment is described in detail based on an Example and a comparative example, this embodiment is not limited to the following Example. The evaluation methods used in this example are as follows. Moreover, the part and% in a present Example are a mass reference | standard unless there is particular notice.

[Density of resin used in this embodiment]
The density of the resin used in this embodiment was measured according to JIS-K-7112.

[MFR of resin used in this embodiment]
The MFR of the resin used in this embodiment was measured according to JIS-K-7210.

[Gel fraction]
A sample (resin-sealed sheet) was extracted for 12 hours in boiling p-xylene, and the proportion of the insoluble portion was calculated as the gel fraction by the following formula. The calculated gel fraction was used as a measure for the degree of crosslinking of the resin-encapsulated sheet.
Gel fraction (mass%) = (sample weight after extraction / sample weight before extraction) × 100

[Heat shrinkage]
The resin sealing sheets obtained in Examples and Comparative Examples were cut into a square of 10 cm in MD direction × 10 cm in TD direction to obtain a test piece. The obtained test pieces were immersed in warm water of 60 ° C. or 90 ° C. for 5 minutes, respectively, and the lengths of the test pieces in the MD direction after immersion were measured. From the length of the obtained test piece after immersion and the length of the test piece before immersion, 60 ° C. and 90 ° C. heat shrinkage rates were calculated according to the following formulas.

[Porosity P (V _H / V _A × 100%)]
The resin sealing sheets obtained in Examples and Comparative Examples were cut into a square of 10 cm in the MD direction and 10 cm in the TD direction, and the mass was measured. By measuring the maximum thickness of the cut sheet, the porosity P was calculated according to the following formula.
P (%) = 100−W / (ρ × t _max × 10 ⁶ ) × 100
(Where P: porosity, W: weight per 1 m ^{2 of} sheet (g / m ² ), t _max : maximum sheet thickness (mm), ρ: specific gravity of sheet (g / mm ³ ). )

[Haze and total light transmittance]
As a sample for measurement, an LM50 type vacuum laminating apparatus (NPC) was stacked in the order of a glass plate for solar cells (white glass 5 cm × 10 cm square: thickness 3 mm manufactured by AGC) / resin sealing sheet / glass plate for solar cells. A vacuum-laminated material was prepared at 150 ° C. The haze and total light transmittance of this measurement sample were measured according to ASTM D-1003.

[Peel strength from glass]
As a sample for measurement, an LM50 type vacuum laminating apparatus (NPC) was stacked in the order of a glass plate for solar cells (white glass 5 cm × 10 cm square: thickness 3 mm manufactured by AGC) / resin sealing sheet / glass plate for solar cells. A vacuum-laminated material was prepared at 150 ° C. The two glass plates for solar cells of this measurement sample were peeled off by hand, and the peel strength between the glass plate and the resin sealing sheet was evaluated as follows.
(Evaluation criteria for peel strength)
○: Strongly adhered and does not peel off by hand (good).
X: It peels by hand (defective).

[Stacking evaluation]
Glass plate for solar cell (white glass manufactured by AGC: thickness 3 mm) / resin sealing sheet / power generation part (single crystal silicon cell (thickness 250 μm)) / resin sealing sheet / back sheet Workability was evaluated. As a back sheet, a laminated film of PVF (38 μm), PET (75 μm), and PVF (38 μm) was used.
(Evaluation criteria for stackability)
○: Easy positioning when stacking (good).
(Triangle | delta): It takes time for positioning when stacking (slightly poor).
X: Positioning during stacking is difficult (defect).
Here, at the time of positioning, the sheet was moved so as to slide on the glass or the power generation part. A case where slippage is poor due to a high coefficient of friction is regarded as “difficult to position”. A case where the positioning took a long time because the slip was slightly bad was defined as “a positioning takes a long time”. Further, the case where sliding was good was regarded as “easy positioning”.

[Example 1]
A three-layer sheet laminated in the order of the surface layer, the inner layer and the surface layer was produced as follows. In addition, ratio of the thickness of a surface layer, an inner layer, and a surface layer was 1: 8: 1 in order. The resin composition containing the following resin and the following additive was used for the surface layer and the inner layer.

  First, two types of the resin composition for the surface layer and the resin composition for the inner layer were melted using two extruders. Then, from the T die connected to the extruder, the above two types of resin compositions are melt-extruded into a sheet shape, rapidly cooled using an embossed cooling roll, and the two-layer three-layer resin seal of Example 1 having a thickness of 600 μm. A stop sheet was prepared. The winding speed of the resin sealing sheet was 4.5 m / min. The ratio of the resin extrusion speed and the resin sealing sheet winding speed during extrusion (sheet winding speed / resin extrusion speed) was 1.2.

[Resin contained in the surface layer]
As the resin contained in the surface layer, 99.1% by mass of linear ultra-low density polyethylene (Affinity EG8100, MFR = 1, density = 0.870 g / cm ³ manufactured by Dow) was used.

[Resin contained in the inner layer]
As the resin contained in the inner layer, 99.6% by mass of linear ultra-low density polyethylene (Affinity EG8100, MFR = 1, density = 0.870 g / cm ³ manufactured by Dow) was used.

[Additives contained in the surface layer]
As additives in the surface layer, 0.5% by mass of γ-methacryloxypropyltrimethoxysilane, 0.2% by mass of 2-hydroxy-4-octoxybenzophenone, n-octadecyl- (4-hydroxy-3,5-diter Shaributylphenyl) propionate 0.1% by weight and bis (2,2,6,6-tetramethyl-4-piperidinyl) sebacate 0.1% by weight were used.

[Additives contained in the inner layer]
As additives in the inner layer, 0.2% by mass of 2-hydroxy-4-octoxybenzophenone, 0.1% by mass of n-octadecyl- (4-hydroxy-3,5-ditertiarybutylphenyl) propionate, bis (2 , 2,6,6-tetramethyl-4-piperidinyl) sebacate 0.1% by weight was used.

  The resin-encapsulated sheet of Example 1 obtained as described above was subjected to electron beam cross-linking treatment at an acceleration voltage of 750 kV and an irradiation density of 60 kGy using EPS-800 (manufactured by Nissin High Voltage). Each characteristic was evaluated as described above for the resin-encapsulated sheet after the electron beam crosslinking treatment. The evaluation results are shown in Table 1.

[Example 2]
Except for adding 10% by mass of maleic anhydride-modified polyethylene (Mitsui Chemicals Admer SE800 MFR = 4.4, density = 0.900 g / cm 3) instead of 0.5% by mass of γ-methacryloxypropyltrimethoxysilane Performed the same operation as Example 1, produced the resin sealing sheet of Example 2, and performed the electron beam bridge | crosslinking process. The above characteristics were evaluated for the resin-encapsulated sheet of Example 2. The evaluation results are shown in Table 1.

[Example 3]
The same operation as in Example 1 was performed except that 1.2% by mass of 2,5-dimethyl-2,5-bis (t-butylperoxy) hexane was further added to the surface layer and the inner layer. A resin sealing sheet was produced. The resin sealing sheet of Example 3 was not irradiated with an electron beam. The above characteristics were evaluated for the resin-encapsulated sheet of Example 3. The gel fraction of the resin sealing sheet of Example 3 was 0%, but the gel fraction of the sealing material portion of the measurement sample for which the peel strength from glass was measured was 63%.

[Comparative Example 1]
As resin contained in the surface layer and the inner layer, instead of resin linear ultra-low density polyethylene, an ethylene / vinyl acetate copolymer (Ultrasen 750 V _A = 32%, MFR = 10, density = 0.904 g / manufactured by Tosoh Corporation) Except having used cm3), operation similar to Example 1 was performed, the resin sealing sheet of the comparative example 1 was produced, and the electron beam bridge | crosslinking process was carried out. The above characteristics were evaluated for the resin-encapsulated sheet of Comparative Example 1. The resin sealing sheet of Comparative Example 1 was inferior in stackability.

[Comparative Example 2]
Except for using a different embossed cooling roll and setting the porosity P to 4.3%, the same operation as in Example 1 was performed to produce a resin-encapsulated sheet of Comparative Example 2, and an electron beam cross-linking treatment was performed. did. The above characteristics were evaluated for the resin-encapsulated sheet of Comparative Example 2. The resin sealing sheet obtained in Comparative Example 2 was inferior in stackability.

[Comparative Example 3]
The same operation as in Example 1 was performed except that different cooling rolls with embossing were used and the porosity P was 81%, and a resin-encapsulated sheet of Comparative Example 3 was produced and subjected to electron beam crosslinking treatment. The above characteristics were evaluated for the resin-encapsulated sheet of Comparative Example 3. The resin sealing sheet obtained in Comparative Example 3 was inferior in heat shrinkage at 60 ° C. and 90 ° C.

  From the description in Table 1, it was found that if the heat shrinkage (90 ° C.) is within a predetermined value, problems such as cell displacement can be prevented.

  The resin sealing sheet for solar cells of the present invention has industrial applicability as a sealing sheet for solar cells.

Claims (3)

Including at least one resin selected from the group consisting of polyethylene resins, polypropylene resins, polybutene resins,
A recess is provided on at least one side,
The percentage V _H / V _A × 100% of the total volume V _{H of the} recesses per unit area and the apparent volume V _A obtained by multiplying the unit area by the maximum thickness is 5 to 80%.
Resin encapsulating sheet for solar cells.   The solar cell resin-encapsulated sheet according to claim 1, wherein the layer containing the resin is subjected to ionizing radiation irradiation treatment and has a gel fraction of 1 to 65 mass%.   The resin sealing sheet for solar cells according to claim 1 or 2, wherein the thermal shrinkage at 90 ° C is 15% or less.