JP7462736B2 - Solar cell encapsulant sheet and method for producing same - Google Patents

Description

The present invention relates to a solar cell encapsulant sheet and a manufacturing method thereof, and more specifically, to a solar cell encapsulant sheet and a manufacturing method thereof that maintains its performance even at high temperatures and has excellent productivity.

As global environmental and energy issues become more serious, solar cells are attracting attention as a means of generating clean, inexhaustible energy. When solar cells are used outdoors, such as on the roofs of buildings, they are generally used in the form of solar cell modules.

A solar cell module is formed by sealing a solar cell element with a solar cell encapsulant sheet and integrating it with a solar cell module protective sheet as necessary. For example, to obtain a crystalline solar cell module, first, a laminate is formed by laminating the following in order: solar cell module protective sheet (front side transparent protective member)/solar cell encapsulant sheet/crystalline solar cell element/solar cell encapsulant sheet/solar cell module protective sheet (rear side protective member). The resulting laminate is then compressed and heated to be integrated. The solar cell encapsulant is then cross-linked and cured to produce a solar cell module.

As the material for the solar cell encapsulant sheet, polyolefin resins such as ethylene-α-olefin copolymers are preferably used from the viewpoints of transparency, insulating properties, flexibility, cost, etc.
Solar cell modules using solar cell encapsulant sheets containing polyolefin resin as a main component may develop bubbles or bulge when exposed to high temperatures, and a solution to this problem was sought from the standpoint of the performance, appearance, durability, etc. of the solar cell module.

In addition, in solar cell encapsulant sheets mainly composed of polyolefin resin, additives such as crosslinking agents and crosslinking assistants may segregate in the sheet, and it may take a considerable amount of time to impregnate the polyolefin resin in advance, and solving these problems is a technical problem. In order to solve this, it has been proposed to further add additives from an injection nozzle installed between the supply port and the tip of the screw of the extruder in the process of melt-kneading a resin composition containing a polyolefin resin and the above-mentioned additives in an extruder (see, for example, Patent Document 1, etc.).
However, the provision of such direct order equipment increases costs, and there has been a demand for a polyolefin-based solar cell encapsulant sheet that can be produced in a relatively short time using a standard extrusion molding machine that is not equipped with direct order equipment.

International Publication No. 2013/161273 A1 Brochure

In view of the above demand, an object of the present invention is to provide a solar cell encapsulant sheet containing a polyolefin resin as a main component, which can effectively suppress the generation of bubbles and swelling at high temperatures in a solar cell module using the same, and a method for producing the same.
A further object of the present invention is to improve productivity, for example, by enabling production in a relatively short period of time using a standard extruder.

As a result of extensive research, the inventors discovered that the above problems could be solved by using a cross-linking agent having a specific chemical structure in combination with a specific cross-linking assistant, and thus completed the present invention.

That is, the first invention of the present application is
[1]
A step of preparing crosslinkable resin pellets by impregnating a crosslinking agent and a crosslinking assistant into pellets mainly composed of a polyolefin resin;
a step of feeding the crosslinkable resin pellets into a cylinder of an extrusion molding machine through a supply port thereof, and melt-kneading a resin composition containing the polyolefin resin, the crosslinking agent, and the crosslinking auxiliary in the cylinder;
extruding the resin composition into a sheet shape from a die of the extruder;
A method for producing a solar cell encapsulant sheet, comprising:
The crosslinking agent contains a compound having two or more alkylperoxy groups represented by the following formula (1) in the structure: R ¹ -OO- -(1)
(wherein R ¹ represents an alkyl group having 1 to 6 carbon atoms).
The above-mentioned production method, wherein the crosslinking coagent comprises triallyl isocyanurate.

Below, [2] to [6] are each preferred embodiments of the first aspect of the present invention.
[2]
The method according to [1], wherein the time for producing the crosslinkable resin pellets is 100 minutes or less.
[3]
The method according to [1] or [2], wherein the compound having two or more alkylperoxy groups in the structure is blended in an amount of 0.4 parts by mass or more per 100 parts by mass of the polyolefin resin.
[4]
The method according to any one of [1] to [3], wherein the compound having two or more alkylperoxy groups in the structure has a structure in which the two or more alkylperoxy groups are bonded to the same carbon atom or bonded via two or more carbon atoms.
[5]
The method according to any one of [1] to [4], wherein the polyolefin resin is substantially free of structural units derived from vinyl acetate.
[6]
The manufacturing method according to any one of [1] to [5], which produces a solar cell encapsulant sheet having a gel fraction of 40% or more after encapsulating a solar cell.

That is, the second invention of the present application is as follows:
[7]
Polyolefin resin,
A compound having two or more alkylperoxy groups represented by the following formula (1) in its structure:
R ¹ -OO- -(1)
(wherein R ¹ represents an alkyl group having 1 to 6 carbon atoms), and

Below, [8] to [10] are each preferred embodiments of the second aspect of the present invention.
[8]
The crosslinkable resin composition according to [7], wherein the compound having two or more alkylperoxy groups is mixed in an amount of 0.4 parts by mass or more per 100 parts by mass of the polyolefin resin.
[9]
The crosslinkable resin composition according to [7] or [8], wherein the compound having two or more alkylperoxy groups in the structure has a structure in which the two or more alkylperoxy groups are bonded to the same carbon atom or bonded via two or more carbon atoms.
[10]
The crosslinkable resin composition according to any one of [7] to [9], wherein the polyolefin resin is substantially free of structural units derived from vinyl acetate.

That is, the third invention of the present application is as follows:
[11]
Polyolefin resin,
A compound having two or more alkylperoxy groups represented by the following formula (1) in its structure:
R ¹ -OO- -(1)
(wherein R ¹ represents an alkyl group having 1 to 6 carbon atoms), and triallyl isocyanurate.
, regarding.

Below, [12] to [16] are each preferred embodiments of the third invention of the present application.
[12]
The solar cell encapsulant sheet according to [11], wherein the compound having two or more alkylperoxy groups is blended in an amount of 0.4 parts by mass or more per 100 parts by mass of the polyolefin resin.
[13]
The solar cell encapsulant sheet according to [11] or [12], wherein the compound having two or more alkylperoxy groups in the structure has a structure in which the two or more alkylperoxy groups are bonded to the same carbon atom or bonded via two or more carbon atoms.
[14]
The solar cell encapsulant sheet according to any one of [11] to [13], wherein the polyolefin resin is substantially free of structural units derived from vinyl acetate.
[15]
A solar cell module comprising a crosslinked and cured product of the solar cell encapsulant sheet according to any one of [11] to [14].
[16]
a step of encapsulating a solar cell with the solar cell encapsulant sheet according to any one of [11] to [14], and a step of crosslinking and curing the solar cell encapsulant sheet;
The method for manufacturing a solar cell module comprising the steps of:

According to the present invention, a high-quality polyolefin-based solar cell encapsulant sheet is provided that can effectively suppress problems such as the generation of bubbles and swelling even when used at high temperatures in a solar cell module. Furthermore, the solar cell encapsulant sheet of the present invention can be produced in a relatively short time using a standard extrusion molding machine, and is therefore of great practical value, being excellent in terms of cost and productivity.

FIG. 2 is a schematic diagram showing an example of the manufacturing method of the first invention of the present application. FIG. 1 is a schematic diagram showing a manufacturing method of the prior art. FIG. 2 is a schematic diagram illustrating a method for evaluating high-temperature durability in one embodiment of the present invention.

Hereinafter, an embodiment of the present invention will be described.
The first invention of the present application is
A step of preparing crosslinkable resin pellets by impregnating a crosslinking agent and a crosslinking assistant into pellets mainly composed of a polyolefin resin;
a step of feeding the crosslinkable resin pellets into a cylinder of an extrusion molding machine through a supply port thereof, and melt-kneading a resin composition containing the polyolefin resin, the crosslinking agent, and the crosslinking auxiliary in the cylinder;
extruding the resin composition into a sheet shape from a die of the extruder;
A method for producing a solar cell encapsulant sheet, comprising:
The crosslinking agent contains a compound having two or more alkylperoxy groups represented by the following formula (1) in the structure: R ¹ -OO- -(1)
(wherein R ¹ represents an alkyl group having 1 to 6 carbon atoms).
The above-mentioned production method, wherein the crosslinking coagent contains triallyl isocyanurate.
That is, in the first invention of the present application, a solar cell encapsulant sheet is produced using at least a polyolefin resin, a crosslinking agent containing a specific component, and a crosslinking aid containing a specific component. In the first invention of the present application, components other than the polyolefin resin, the crosslinking agent, and the crosslinking aid, for example, other additives, can be used as optional components.
Each material used in the manufacturing method of the first aspect of the present invention will be described in detail below.

Polyolefin Resin The polyolefin resin used in the first invention of the present application may be a polymer having a structural unit derived from an olefin having two or more carbon atoms, and is not otherwise particularly limited. Suitable examples thereof include low-density ethylene resins, medium-density ethylene resins, very low-density ethylene resins, propylene (co)polymers, 1-butene (co)polymers, 4-methylpentene-1 (co)polymers, ethylene-α-olefin copolymers, ethylene-cyclic olefin copolymers, ethylene-α-olefin-cyclic olefin copolymers, ethylene-α-olefin-non-conjugated polyene copolymers, ethylene-α-olefin-conjugated polyene copolymers, ethylene-aromatic vinyl copolymers, and ethylene-α-olefin-aromatic vinyl copolymers.
These polyolefin resins may be used alone or in combination of two or more.

Polyolefin-based resins may or may not contain structural units derived from vinyl acetate. However, it has been considered relatively difficult to uniformly impregnate crosslinking agents and crosslinking aids with polyolefin-based resins that do not substantially contain structural units derived from vinyl acetate. Therefore, applying the first invention of this application to polyolefin-based resins that do not substantially contain structural units derived from vinyl acetate is of particularly high technical value.

Among the various polyolefin resins listed above, ethylene-α-olefin copolymers having structural units derived from ethylene and α-olefins having 3 to 20 carbon atoms are preferred because they offer an excellent balance of properties required for solar cell encapsulation materials, such as transparency, adhesion, flexibility, heat resistance, appearance, crosslinking properties, electrical properties, and extrusion moldability.

The melt flow rate (MFR) of the polyolefin resin used in the first invention of this application, measured in accordance with ASTM D1238 under conditions of 190°C and a load of 2.16 kg, is usually 0.1 g/10 min to 50 g/10 min, preferably 2 g/10 min to 40 g/10 min, more preferably 2 g/10 min to 30 g/10 min, and even more preferably 5 g/10 min to 10 g/10 min. The MFR of the polyolefin resin can be adjusted by adjusting the polymerization temperature and polymerization pressure during the polymerization reaction, as well as the molar ratio of the monomer concentration of ethylene, etc. and the hydrogen concentration in the polymerization system.

When the MFR is 0.1 g/10 min or more and less than 10 g/10 min, the sheet can be easily produced by calendar molding. When the MFR is 0.1 g/10 min or more and less than 10 g/10 min, the fluidity of the resin composition containing the ethylene-α-olefin copolymer is low, which is preferable in that it is possible to effectively prevent the lamination device from being soiled by the molten resin that protrudes when laminating the sheet and the battery element.

Furthermore, when the MFR is 2 g/10 min or more, preferably 4 g/10 min or more, and more preferably 10 g/10 min or more, the fluidity of the resin composition containing the ethylene-α-olefin copolymer is improved, thereby improving productivity during sheet extrusion molding.

In addition, if unevenness occurs on the sheet surface, the adhesion between the sheet and the front-side transparent protective member, the cell, the electrode, and the back-side protective member during lamination processing of the solar cell module is deteriorated, resulting in insufficient adhesion. However, if the MFR is set to 50 g/10 min or less, the molecular weight increases, making it easier to mold into a sheet of uniform thickness, and these problems can be more effectively suppressed. In addition, since adhesion to the roll surface of a chill roll or the like can be effectively suppressed, the need for a peeling process or the like is reduced, which can contribute to improving productivity and reducing costs. Furthermore, since the resin composition has so-called "toughness," it is easier to mold a thick sheet of 0.1 mm or more. In addition, since the crosslinking properties during lamination processing of the solar cell module are improved, sufficient crosslinking can be performed, and the decrease in heat resistance can be more effectively suppressed.
When the MFR is 27 g/10 min or less, drawdown during sheet molding can be effectively suppressed, a wide sheet can be molded, and the crosslinking properties and heat resistance are further improved, making it possible to obtain a particularly good solar cell encapsulant sheet.

The polyolefin resin used in the first invention of the present application preferably has a density in the range of 0.865 to 0.884 g/ ^cm3 as measured in accordance with ASTM D1505. The density of the polyolefin resin can be adjusted by the content ratio of structural units derived from ethylene. That is, by increasing the content ratio of ethylene units, the crystallinity becomes high, and a polyolefin resin with high density can be obtained. On the other hand, by decreasing the content ratio of structural units derived from ethylene, the crystallinity becomes low, and a polyolefin resin with low density can be obtained.

When the density of the polyolefin resin is 0.884 g/ ^cm3 or less, the crystallinity is low and the transparency can be increased. Furthermore, extrusion molding at low temperatures is easy, and extrusion molding can be performed at, for example, 130°C or less. Therefore, even if an organic peroxide is kneaded into the polyolefin resin, the crosslinking reaction in the extruder can be prevented from progressing. In addition, since the polyolefin resin has high flexibility, the occurrence of cracks in the solar cell element cells and chipping of the thin film electrodes during lamination molding of the solar cell module can be more effectively prevented.

On the other hand, when the density of the polyolefin resin is 0.865 g/ ^cm3 or more, the crystallization speed of the polyolefin resin can be increased, so that the sheet extruded from the extruder is less sticky and can be easily peeled off with the first cooling roll, and the solar cell encapsulant sheet can be obtained with high productivity. In addition, since the sheet is less likely to become sticky, the occurrence of blocking can be suppressed and the sheet can be easily unwound. In addition, since the resin is sufficiently crosslinked, the decrease in heat resistance can be effectively suppressed.

The polyolefin resin used in the first invention of the present application has a Shore A hardness measured in accordance with ASTM D2240 of preferably 60 to 85, more preferably 62 to 83, even more preferably 62 to 80, and particularly preferably 65 to 80. The Shore A hardness of the polyolefin resin can be adjusted by controlling the content ratio of ethylene units and the density of the polyolefin resin within the above-mentioned numerical range. That is, a polyolefin resin having a high content ratio of ethylene units and a high density has a high Shore A hardness. On the other hand, a polyolefin resin having a low content ratio of ethylene units and a low density has a low Shore A hardness. The Shore A hardness is measured after 15 seconds or more have elapsed since the test piece sheet was loaded.

If the Shore A hardness is 60 or more, the polyolefin resin is less sticky and blocking can be suppressed. In addition, when processing the solar cell encapsulant into a sheet, the sheet can be easily unwound and the deterioration of heat resistance can be suppressed.

On the other hand, if the Shore A hardness is 85 or less, the crystallinity is low and the transparency can be increased. Furthermore, because of its high flexibility, it is possible to prevent cracking of the cells, which are the solar cell elements, and chipping of the thin-film electrodes during lamination molding of the solar cell module.

Ethylene/α-olefin copolymers preferably used as polyolefin resins preferably have structural units derived from ethylene and structural units derived from an α-olefin having 3 to 20 carbon atoms. Such ethylene/α-olefin copolymers are obtained, for example, by copolymerizing ethylene with an α-olefin having 3 to 20 carbon atoms. As the α-olefin, one type of α-olefin having 3 to 20 carbon atoms can usually be used alone or two or more types can be used in combination. Among these, α-olefins having 10 or less carbon atoms are preferred, and α-olefins having 3 to 8 carbon atoms are particularly preferred.

Specific examples of such α-olefins include propylene, 1-butene, 1-pentene, 1-hexene, 3-methyl-1-butene, 3,3-dimethyl-1-butene, 4-methyl-1-pentene, 1-octene, 1-decene, and 1-dodecene. Among these, propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, and 1-octene are preferred due to their ease of availability. The ethylene-α-olefin copolymer may be a random copolymer or a block copolymer, but a random copolymer is preferred from the viewpoint of flexibility.

The proportion of structural units derived from an α-olefin having 3 to 20 carbon atoms (hereinafter also referred to as "α-olefin units") contained in the ethylene/α-olefin copolymer used in this embodiment is preferably 10 to 20 mol %.
When the proportion of the α-olefin unit is 10 mol % or more, a sheet having high transparency can be easily obtained. In addition, extrusion molding can be easily performed at low temperatures, for example, at 130° C. or less.
Therefore, even when the ethylene-α-olefin copolymer is impregnated with a crosslinking agent, the crosslinking reaction in the extruder can be suppressed. In addition, since the copolymer has an appropriate flexibility, it is possible to effectively prevent the occurrence of cracks in the solar cell element and chipping of the thin-film electrode during lamination molding of the solar cell module.

When the content of α-olefin units is 20 mol% or less, the crystallization speed of the ethylene-α-olefin copolymer becomes appropriate, so the sheet extruded from the extruder does not become sticky and is easy to peel off with the first cooling roll, making it possible to obtain a sheet-like solar cell encapsulant more efficiently. In addition, because the sheet does not become sticky, blocking can be effectively prevented and the sheet has good payout properties. In addition, a decrease in heat resistance can be effectively prevented.

It is particularly preferable that the ethylene/α-olefin copolymer used in the present embodiment satisfies the following requirements a1 to a4.
a1) The content of structural units derived from ethylene is 80 to 90 mol %, and the content of structural units derived from an α-olefin having 3 to 20 carbon atoms is 10 to 20 mol %.
a2) The MFR measured in accordance with ASTM D1238 at 190° C. under a load of 2.16 kg is 2 to 40 g/10 min.
a3) The density, measured in accordance with ASTM D1505, is 0.865 to 0.884 g/ ^cm3 .
a4) Shore A hardness, measured in accordance with ASTM D2240, is 60 to 85.

Crosslinking Agent The crosslinking agent used in the first invention of the present application includes a compound having two or more alkylperoxy groups represented by the following formula (1) in its structure (hereinafter also referred to as "specific peroxide").
R ¹ -OO- -(1)
In the above formula (1), R ¹ represents an alkyl group having 1 to 6 carbon atoms.
By using the specific peroxide as at least a part of the crosslinking agent, the solar cell encapsulant sheet obtained by the manufacturing method of the first invention of the present application can effectively suppress the generation of bubbles and swelling at high temperatures. In addition, since this crosslinking agent has excellent permeability into polyolefin resins, it is possible to manufacture a solar cell encapsulant sheet having good performance in a relatively short time using a standard extrusion molding machine, which contributes to improving productivity and reducing costs.

By crosslinking the polyolefin resin, a solar cell module with excellent heat resistance and adhesiveness can be obtained. In addition, when a silane coupling agent is used, a crosslinking agent is used in combination with the polyolefin resin to graft-modify the polyolefin resin with the silane coupling agent, thereby obtaining a solar cell encapsulant sheet with good adhesiveness to other members such as a front transparent protective member, a back protective member, a cell, and an electrode.
The amount of the crosslinking agent used is not particularly limited and can be appropriately set depending on the various performances required of the solar cell encapsulant sheet and the various conditions of the manufacturing process. However, it is preferable to use an amount such that the gel fraction after encapsulating the solar cell becomes 40% or more in combination with a specific crosslinking assistant described later.
More specifically, from the viewpoint of sufficient crosslinking, the specific peroxide is preferably 0.4 parts by mass or more per 100 parts by mass of the polyolefin resin, more preferably 0.4 to 3.0 parts by mass, and particularly preferably 0.4 to 1.5 parts by mass, per 100 parts by mass of the polyolefin resin.
When the content of the crosslinking agent is equal to or more than the lower limit, the deterioration of the crosslinking properties of the encapsulating sheet is suppressed, and the graft reaction of the silane coupling agent to the main chain of the crosslinkable resin described later is improved, so that the deterioration of the heat resistance and adhesiveness can be suppressed. Also, when the content of the crosslinking agent is equal to or less than the upper limit, the generation amount of the decomposition products of the crosslinking agent is further reduced, and the generation of bubbles in the encapsulating sheet can be more reliably suppressed.

R ¹ -OO- -(1)
In the alkylperoxy group represented by formula (1) contained in the specific peroxide, R ¹ is an alkyl group having 1 to 6 carbon atoms, and although there is no other limitation, it is preferably an alkyl group having 3 to 6 carbon atoms.
R ¹ may be linear or branched, but is preferably a bulky group from the viewpoint of the stability of the specific peroxide, and therefore is often preferably branched. A particularly preferred example is a t-butyl group.

The specific peroxide is not particularly limited in terms of its chemical structure as long as it has two or more alkylperoxy groups represented by the following formula (1), but it is preferable that the specific peroxide has a structure in which the two or more alkylperoxy groups are bonded to the same carbon atom or bonded via two or more carbon atoms.

In specific peroxides in which two or more alkylperoxy groups are bonded to the same carbon atom, there is no particular restriction on the carbon atom, but it is preferably one of the carbon atoms constituting a cycloalkane, chain alkane, or ester having 1 to 18 carbon atoms. Suitable examples of such specific peroxides include 1,1-di(t-butylperoxy)cyclohexane, 2,2-di(t-butylperoxy)butane, and n-butyl-4,4-di(t-butylperoxy)valerate.

In the specific peroxide in which two or more alkylperoxy groups are bonded via two or more carbon atoms, the structure having two or more carbon atoms is not limited, but is preferably an alkylene group. In this case, the alkylene group is also not particularly limited, but is preferably a linear or branched alkylene group having 1 to 18 carbon atoms. In place of the alkylene group, a structure in which a part of the alkylene group structure is substituted with an aromatic ring or a structure containing a triple bond may be used.
Suitable examples of such specific peroxides include 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3, and the like.

From the viewpoint of the balance between the productivity in extrusion sheet molding and the crosslinking rate during lamination molding of the solar cell module, the one-minute half-life temperature of the specific peroxide is preferably 140 to 200°C.
When the one-minute half-life temperature of the specific peroxide is 140° C. or higher, the progress of the crosslinking reaction of the solar cell encapsulant during extrusion sheet molding can be effectively suppressed. When the one-minute half-life temperature of the organic peroxide is 200° C. or lower, the crosslinking speed during laminate molding of the solar cell module is sufficient, so that the productivity of the solar cell module can be improved. In addition, it is easy to ensure the heat resistance and adhesiveness of the solar cell encapsulant.

These specific peroxides may be used alone or in combination of two or more. In addition, only the specific peroxide may be used as a crosslinking agent, or the specific peroxide may be used in combination with another crosslinking agent. When the specific peroxide is used in combination with another crosslinking agent, the ratio of the specific peroxide in the total crosslinking agent is preferably 80% by mass or more, and particularly preferably 90% by mass or more. There are no particular limitations on the type of the other crosslinking agent, but it is preferable that the other crosslinking agent is a peroxide that does not fall under the category of a specific peroxide.

Crosslinking Auxiliary Agent In the first invention of the present application, in order to promote the crosslinking reaction and increase the degree of crosslinking of the polyolefin resin, the pellets mainly composed of the polyolefin resin are impregnated with a crosslinking auxiliary agent.
The crosslinking aid used in the first invention of the present application includes triallyl isocyanurate. Triallyl isocyanurate, in combination with a crosslinking agent containing a specific peroxide, can sufficiently crosslink a polyolefin resin with a relatively small amount, so that productivity and the quality of the produced solar cell encapsulant sheet can be compatible at a high level.
In the present invention, triallyl isocyanurate alone may be used as a crosslinking aid, or triallyl isocyanurate may be used in combination with other crosslinking aids. When triallyl isocyanurate is used in combination with other crosslinking aids, the proportion of triallyl isocyanurate in the total crosslinking aids is preferably 50% by mass or more, and particularly preferably 80% by mass or more.
The type of the other crosslinking auxiliary is not particularly limited, but a conventionally used compound having two or more double bonds in the molecule can be preferably used, and a compound having three or more double bonds in the molecule is more preferable.

The amount of triallyl isocyanurate used can be appropriately set depending on the performance required for the solar cell encapsulant sheet and the conditions of the manufacturing process, but it is preferable to use an amount that, in combination with a specific crosslinking agent, results in a gel fraction of 40% or more after encapsulating the solar cell. More specifically, it is more preferable that the amount is 0.1 to 1.0 part by mass, and particularly preferably 0.1 to 0.4 part by mass, relative to 100 parts by mass of the polyolefin resin.
By setting the amount of triallyl isocyanurate used within the above range, impregnation can be achieved relatively easily and in a short time, which not only provides excellent productivity but also provides a solar cell encapsulant having an appropriate crosslinked structure, thereby improving the heat resistance, mechanical properties, and adhesiveness of the solar cell encapsulant.

Other Additives In the method for producing a solar cell encapsulant sheet according to the first aspect of the present invention, in addition to the above-mentioned crosslinking agent and crosslinking aid, various other additives can be appropriately used within the scope of the present invention. For example, one or more additives selected from silane coupling agents, ultraviolet absorbers, light stabilizers, antioxidants, various resins other than polyolefin resins, various rubbers, plasticizers, fillers, pigments, dyes, antioxidants, antistatic agents, antibacterial agents, antifungal agents, flame retardants, light diffusing agents, discoloration inhibitors, and dispersants can be appropriately added.

The use of silane coupling agents is useful for improving adhesion to substrates, protective sheets, solar cell elements, etc. For example, compounds having a hydrolyzable group such as an alkoxy group along with an amino group or an epoxy group can be mentioned. Specifically, vinyltriethoxysilane, vinyltrimethoxysilane, vinyltris(β-methoxyethoxysilane), γ-glycidoxypropyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, etc. can be used. Preferred are γ-glycidoxypropylmethoxysilane, γ-aminopropyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, and vinyltriethoxysilane, which have good adhesive properties. These silane coupling agents may be used alone or in combination of two or more.

The amount of silane coupling agent added varies depending on the type of silane coupling agent, but is preferably 0.1 to 4 parts by weight, and more preferably 0.1 to 3 parts by weight, per 100 parts by weight of polyolefin resin. When the amount is equal to or greater than the lower limit, the adhesion of the solar cell encapsulant sheet is excellent. When the amount is equal to or less than the upper limit, the balance between cost and performance of the solar cell encapsulant sheet is excellent.

Preferred examples of ultraviolet absorbents include benzophenone-based agents such as 2-hydroxy-4-normal-octyloxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2,2-dihydroxy-4-methoxybenzophenone, 2-hydroxy-4-methoxy-4-carboxybenzophenone, and 2-hydroxy-4-N-octoxybenzophenone; benzotriazole-based agents such as 2-(2-hydroxy-3,5-di-t-butylphenyl)benzotriazole and 2-(2-hydroxy-5-methylphenyl)benzotriazole; and salicylic acid ester-based agents such as phenyl salicylate and p-octylphenyl salicylate. These ultraviolet absorbents may be used alone or in combination of two or more.

The amount of UV absorber added varies depending on the type of UV absorber, but is preferably 0.005 to 5 parts by weight per 100 parts by weight of polyolefin resin. If the amount of UV absorber added is within the above range, it is preferable because it can sufficiently ensure the effect of improving weather resistance stability and prevent a decrease in the transparency of the solar cell encapsulant and adhesion to the front transparent protective member, back protective member, cell, electrode, and aluminum.

As light stabilizers, hindered amine type and hindered piperidine type compounds such as bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate and 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}] are preferably used. These light stabilizers may be used alone or in combination of two or more.

The amount of light stabilizer added varies depending on the type of light stabilizer, but is preferably 0.005 to 5 parts by weight per 100 parts by weight of polyolefin resin. When the amount of light stabilizer added is within the above range, it is preferable because it can sufficiently ensure the effect of improving weather resistance stability and prevent a decrease in the transparency of the solar cell encapsulant and adhesion to the front-side transparent protective member, back-side protective member, cell, electrode, and aluminum.

Specific examples of heat stabilizers include phosphite-based heat stabilizers such as tris(2,4-di-tert-butylphenyl)phosphite, bis[2,4-bis(1,1-dimethylethyl)-6-methylphenyl]ethyl ester phosphorous acid, tetrakis(2,4-di-tert-butylphenyl)[1,1-biphenyl]-4,4'-diyl bisphosphonite, and bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite; lactone-based heat stabilizers such as the reaction product of 3-hydroxy-5,7-di-tert-butyl-furan-2-one and o-xylene; 3,3',3",5,5',5"-hexa-tert-butyl-a,a',a"-(methylene-2,4,6-triyl)tri-p-cresol, 1,3,5-trimethyl Preferred examples of the heat stabilizer include hindered phenol-based heat stabilizers such as 1,2,4,6-tris(3,5-di-tert-butyl-4-hydroxyphenyl)benzylbenzene, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, and thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]; sulfur-based heat stabilizers; and amine-based heat stabilizers. Among these, phosphite-type heat stabilizers and hindered phenol-type heat stabilizers are preferred. These heat stabilizers may be used alone or in combination of two or more.

The amount of heat stabilizer added varies depending on the type of heat stabilizer, but is preferably 0.005 to 5 parts by weight per 100 parts by weight of polyolefin resin. When the amount of heat stabilizer added is within the above range, the effect of improving resistance to high temperature and humidity, resistance to heat cycles, and heat stability is sufficiently ensured, and a decrease in the transparency of the solar cell encapsulant and adhesion to the front transparent protective member, back protective member, cells, electrodes, and aluminum can be prevented.

Impregnation Step In one step of the method for producing a solar cell encapsulant sheet of the first invention of the present application, a crosslinkable resin pellet is produced by impregnating a pellet mainly composed of a polyolefin resin with a crosslinking agent and a crosslinking assistant.
The shape and size of the pellets are not particularly limited, and shapes and sizes conventionally used in the art may be appropriately adopted, but the average particle size of the pellets is preferably in the range of 0.2 to 10 mm. If the average particle size of the pellets is within the above range, it is preferable because it provides an excellent balance between the stirrability of the pellets, the main component of which is a polyolefin resin, which will be described later, and the impregnation time of the additive into the pellets.

The term "mainly composed of polyolefin resin" means that the polyolefin resin is the component that occupies the largest amount among the components constituting the pellet. The polyolefin resin preferably constitutes 90% by mass or more, and particularly preferably 99% by mass or more, of the pellet.
The method for producing pellets mainly composed of polyolefin resin is not particularly limited, but examples thereof include a method in which a polyolefin resin is melt-kneaded and extruded into a strand or sheet shape using a single-screw or twin-screw extruder, and then cut into pellets of a predetermined particle size using a pelletizer. The pellets may contain additives other than the crosslinking agent and crosslinking aid described above as appropriate in advance, provided that the object of the present invention is not impaired.

In the impregnation step, the pellets mainly composed of a polyolefin resin may be impregnated with a crosslinking agent and a crosslinking auxiliary separately. From the viewpoint of production efficiency and uniform impregnation with both the crosslinking agent and the crosslinking auxiliary, however, it is preferable to mix the crosslinking agent and the crosslinking auxiliary and impregnate the pellets with the mixture.
Since the triallyl isocyanurate used as at least a part of the crosslinking aid has a melting point near room temperature, and most of the specific peroxides used as at least a part of the crosslinking agent are liquid at room temperature or supplied in the form of a high-concentration hydrocarbon solution, it is often possible to form a liquid by mixing the crosslinking agent and the crosslinking aid, and it is also preferable to prepare the liquid in advance in this way and impregnate it into pellets mainly composed of polyolefin resin. When the crosslinking agent and/or the crosslinking aid are solid, a diluting solvent may be added as appropriate to improve the solubility or dispersibility of the solid component.
Additives other than the crosslinking agent and the crosslinking assistant may be added to the impregnation liquid in advance. When the additives other than the crosslinking agent and the crosslinking assistant are solid, a diluting solvent may be appropriately added to improve the solubility or dispersibility of such solid additives.

In this case, the method for dissolving or dispersing the solid components and solid additives is not particularly limited. For example, a liquid crosslinking agent, crosslinking aid, and/or other additives can be placed in a stirring mixer such as a Henschel mixer, tumbler mixer, super mixer, rotary mixer, etc., and a solid crosslinking agent, crosslinking aid, and/or other additives can be added thereto and stirred and mixed to prepare a liquid containing the crosslinking agent and crosslinking aid, as well as other additives if desired.

The temperature for stirring and mixing is not particularly limited, but may be room temperature, or may be heated to about 30 to 50°C to improve stirring efficiency. If the temperature is equal to or higher than the lower limit, the dissolution or dispersion speed of the solid additive can be improved, thereby improving the productivity of the solar cell encapsulant sheet. If the temperature is equal to or lower than the upper limit, deterioration of the additive can be suppressed.
The time for stirring and mixing is not particularly limited, but it is preferable to continue stirring and mixing until the solid components are visually uniformly dissolved or dispersed.
Here, as for components that are liquid at room temperature, many of them are liquid at room temperature, such as crosslinking agents, crosslinking assistants, silane coupling agents, etc. On the other hand, many of them are solid at room temperature, such as ultraviolet absorbers, heat stabilizers, light stabilizers, etc.

As a specific method suitable for impregnating the crosslinking agent and the crosslinking aid into the pellets mainly composed of a polyolefin resin, the following method can be exemplified.
First, pellets mainly composed of a polyolefin resin and a liquid containing a crosslinking agent and a crosslinking aid are fed into a stirring mixer such as a Henschel mixer, a tumbler mixer, a super mixer, or a rotary mixer.
Next, the stirring mixer is stirred to bring the pellets mainly made of polyolefin resin into contact with the liquid, and the pellets are impregnated with the liquid to produce crosslinkable resin pellets. It is preferable to supply the entire amount of the pellets mainly made of polyolefin resin before rotating the stirring mixer. On the other hand, the liquid containing the crosslinking agent and the crosslinking aid may be supplied in its entirety before rotating the stirring mixer, or may be supplied in portions. From the viewpoint of more uniform impregnation into the pellets, it is preferable to supply the entire amount into the stirring mixer. From the viewpoint of shortening the production time, it is preferable to supply the entire amount.
The motor power value of the stirring mixer during stirring and mixing, and the integrated motor power value of the stirring mixer during stirring and mixing are design items that can be determined depending on the impregnation speed and processing amount of the crosslinking agent, crosslinking assistant, etc.

The temperature of the pellets when the crosslinking agent and crosslinking assistant are impregnated into the pellets mainly composed of polyolefin resin is not particularly limited, and may be room temperature, or may be heated to about 30 to 50°C to increase the impregnation speed. If the temperature is equal to or higher than the lower limit, the impregnation speed of the solution containing the additive into the pellets can be improved, thereby improving the productivity of the solar cell encapsulant sheet. If the temperature is equal to or lower than the upper limit, the deterioration of the crosslinking agent, crosslinking assistant, etc. can be further suppressed. Also, the fusion of the pellets with each other and the fusion of the pellets to the stirring mixer can be further suppressed. Note that the temperature of the pellets here refers to the surface temperature of the pellets.

The time for impregnating the crosslinking agent and crosslinking aid into the pellets mainly composed of polyolefin resin, i.e., the time for carrying out the process of preparing crosslinkable pellets, is preferably short from the viewpoint of productivity, and is therefore preferably 100 minutes or less, particularly preferably 60 minutes or less. In the first invention of the present application, the crosslinking agent and crosslinking aid have high impregnation properties into the pellets mainly composed of polyolefin resin, so that the time required for impregnation can be reduced and productivity can be improved in this embodiment as well. This also makes it possible to further suppress deactivation of the crosslinking agent, crosslinking aid, other additives, etc.
In this embodiment, whether the impregnation of the pellets with the crosslinking agent and the crosslinking assistant is completed can be confirmed by the motor power value of the stirring mixer. When the impregnation is completed, the pellets are no longer wet, and the motor power value increases sharply.

According to the manufacturing method of the solar cell encapsulant sheet in this embodiment, the crosslinking agent, crosslinking aid, etc. are pre-impregnated into the pellets mainly composed of polyolefin resin, thereby making it possible to uniformly distribute the crosslinking agent, crosslinking aid, etc. inside the pellets while suppressing deterioration of the crosslinking agent, crosslinking aid, etc. Therefore, it is possible to stably obtain a solar cell encapsulant sheet in which the crosslinking agent, crosslinking aid, etc. are uniformly dispersed within the sheet.
The combination of the specific crosslinking agent and the specific crosslinking aid used in the first invention of the present application has excellent impregnation properties and can be uniformly impregnated into pellets mainly composed of polyolefin resin in a relatively short time, so the manufacturing method of the first invention of the present application can produce a high-quality solar cell encapsulant sheet with high productivity.

Melt-Kneading Step Next, the crosslinkable resin pellets obtained in the above kneading step are fed into a cylinder of an extruder through a supply port, and a resin composition containing the polyolefin resin, the crosslinking agent, and the crosslinking auxiliary is melt-kneaded in the cylinder.
The process is shown diagrammatically in Figure 1. In Figure 1, reference numeral 100 denotes an extrusion molding machine.
In the present embodiment, the extruder 100 may be any of various known twin-screw extruders or single-screw extruders. As the extruder, a twin-screw extruder is preferred because of its excellent kneading performance.

As shown in FIG. 1 , the extrusion molding machine 100 has, for example, a supply port 101 at the most upstream portion through which the crosslinkable resin pellets obtained in the kneading process can be fed into a cylinder 103, a screw 105 is disposed inside the cylinder 103, and a die 109 such as a T-die or a ring die at the most downstream tip.
First, the crosslinkable resin pellets are fed into the cylinder 103 from the feed port 101. Next, the crosslinkable resin pellets fed into the cylinder 103 are heated and melted by a heater disposed outside the cylinder 103, and are melt-kneaded by the rotating screw 105.

In the prior art, the impregnation of the crosslinking agent and crosslinking aid into the polyolefin resin was not necessarily sufficient, so as shown in Fig. 2, an injection nozzle 107 capable of injecting the crosslinking agent and/or crosslinking aid was provided between the supply port 101 and the tip of the screw 105. The crosslinking agent and/or crosslinking aid was supplied to the injection nozzle 107 from a container 201 by using a supply pump 203, for example.
A standard extruder is not provided with the injection nozzle 107, and providing the injection nozzle 107 would significantly increase the cost. In addition, installing the container 201, the supply pump 203, and the associated piping would also increase the cost.
In the first invention of the present application, since the crosslinking agent and crosslinking aid have excellent impregnation properties into the polyolefin resin, an injection nozzle 107 or the like is not required, and the kneading process can be carried out using a standard extrusion molding machine, which can greatly contribute to reducing production costs.

Extrusion Molding Step In the first invention of the present application, the resin composition containing the polyolefin resin, the crosslinking agent, and the crosslinking aid obtained in the melt-kneading step is extruded into a sheet shape from the die of an extruder.
In the extrusion molding step in the embodiment shown in FIG. 1, a resin composition is extruded into a sheet shape from a die 109 of an extruder 100 as described below.

The resin composition is melt-kneaded from a supply port 101 and extruded into a sheet form from a die 109 such as a T-die attached to the tip of an extrusion molding machine 100 to obtain a solar cell encapsulant sheet.
Although the extrusion temperature is not particularly limited, it is preferable to melt-knead the mixture at a temperature lower than the one-hour half-life temperature of the crosslinking agent used and extrude the mixture into a sheet, which can prevent the crosslinking agent from being deactivated.
Specifically, the extrusion temperature (cylinder temperature) is preferably 70 to 130° C. By setting the extrusion temperature to the above lower limit or more, the productivity of the solar cell encapsulant can be improved. Furthermore, by setting the extrusion temperature to the above upper limit or less, the deterioration of the additives can be suppressed. Furthermore, gelation of the solar cell encapsulant can be suppressed.

Thus, in the manufacturing method of the solar cell encapsulant sheet in this embodiment, the additives pass through the extruder 100 only once. This prevents various additives from being deactivated by heating in the extruder 100 or by frictional heat with the screw blades, and allows for the stable manufacture of high-quality solar cell encapsulant sheets.

In order to improve the deaeration properties, after extrusion into a sheet, the surface of the sheet may be embossed.
The method for embossing the surface of the sheet is not particularly limited, but may be, for example, a method in which a sheet extruded from a T-die is fed between an embossing roll having an embossed pattern on its surface and a rubber roll arranged opposite the embossing roll, and the surface of the sheet is embossed while the embossing roll is pressed against the molten sheet. The obtained sheet may be reheated to melt it and then embossed.

From the viewpoint of productivity, it is preferable that the solar cell encapsulant sheet extruded from a T-die or the like is cooled and solidified by a cooling roll while maintaining a uniform thickness, and then wound up by a winding machine 205. In this case, the line speed is preferably high in terms of productivity, and is, for example, preferably 0.5 m/min or more, and more preferably 1 m/min or more.
In this embodiment, the obtained solar cell encapsulant sheet can be used in a sheet form cut to fit the size of the solar cell module, or in a roll form that can be cut to fit the size immediately before producing the solar cell module.

The second invention of the present application is a crosslinkable resin composition ,
Polyolefin resin,
A compound having two or more alkylperoxy groups represented by the following formula (1) in its structure:
R ¹ -OO- -(1)
(wherein R ¹ represents an alkyl group having 1 to 6 carbon atoms), and a crosslinkable resin composition for use in a solar cell encapsulant, comprising triallyl isocyanurate.

The crosslinkable resin composition of the second invention of the present application is a high-quality crosslinkable resin composition in which a combination of a compound having two or more alkylperoxy groups represented by formula (1) in the structure, which functions as a crosslinking agent, and triallyl isocyanurate, which functions as a crosslinking assistant, is impregnated into a polyolefin resin uniformly and in an amount sufficient for good crosslinking, and can be suitably used for solar cell encapsulant applications. A solar cell module formed using the crosslinkable resin composition of the second invention of the present application effectively suppresses problems such as the generation of bubbles and swelling even when used at high temperatures.
In addition, the crosslinkable resin composition of the second invention of the present application is excellent in productivity and can be produced in a relatively short time using a conventionally widely used extrusion molding machine, since it is easy to uniformly and sufficiently impregnate a polyolefin resin with a combination of a compound having two or more alkylperoxy groups represented by formula (1) in the structure functioning as a crosslinking agent and triallyl isocyanurate functioning as a crosslinking auxiliary.

The details of the polyolefin resin, the compound having two or more alkylperoxy groups represented by formula (1) in the structure, and triallyl isocyanurate, which constitute the crosslinkable resin composition of the second invention of this application, and the preferred forms thereof are the same as those described above for the first invention of this application.
The crosslinkable resin composition of the second invention of the present application may contain components other than the polyolefin resin, the compound having two or more alkylperoxy groups represented by formula (1) in the structure, and triallyl isocyanurate, and the details and preferred forms of these components are also the same as those explained above regarding the first invention of the present application.
The preferred composition of the crosslinkable resin composition of the second invention of this application, i.e., the preferred usage ratios of the polyolefin resin, the compound having two or more alkylperoxy groups represented by formula (1) in the structure, and triallyl isocyanurate, and other components used as desired, are the same as those described above for the first invention of this application.

The method for producing the crosslinkable resin composition of the second invention of the present application is not particularly limited, but it is preferably produced by the production method of the first invention of the present application, and it is also preferably produced up to the melt-kneading step of the first invention of the present application.
The shape of the crosslinkable resin composition of the second invention of the present application is not particularly limited, but is preferably in the form of pellets or a sheet. In the case of a sheet shape, the crosslinkable resin composition of the second invention of the present application may also correspond to the solar cell encapsulant sheet of the third invention of the present application.

The third invention of the present application is a solar cell encapsulant sheet .
Polyolefin resin,
A compound having two or more alkylperoxy groups represented by the following formula (1) in its structure:
R ¹ -OO- -(1)
(wherein R ¹ represents an alkyl group having 1 to 6 carbon atoms), and a solar cell encapsulant sheet comprising triallyl isocyanurate.

The solar cell encapsulant sheet of the third invention of the present application is a high-quality solar cell encapsulant sheet in which a combination of a compound having two or more alkylperoxy groups represented by formula (1) in its structure, which functions as a crosslinking agent, and triallyl isocyanurate, which functions as a crosslinking auxiliary, is impregnated into a polyolefin resin uniformly and in an amount sufficient for good crosslinking, and can be suitably used for encapsulating solar cell elements to form a solar cell module.
A solar cell module formed using the solar cell encapsulant sheet of the third invention of the present application effectively prevents problems such as the generation of air bubbles and swelling even when used at high temperatures.
In addition, the solar cell encapsulant sheet of the third invention of the present application is excellent in productivity and can be produced in a relatively short time using a conventionally widely used extrusion molding machine, since it is easy to uniformly and sufficiently impregnate a polyolefin resin with a combination of a compound having two or more alkylperoxy groups represented by formula (1) in its structure, which functions as a crosslinking agent, and triallyl isocyanurate, which functions as a crosslinking auxiliary.

The details of the polyolefin resin, the compound having two or more alkylperoxy groups represented by formula (1) in its structure, and triallyl isocyanurate, which constitute the solar cell encapsulant sheet of the third invention of the present application, and the preferred forms thereof are the same as those described above for the first invention of the present application.
The solar cell encapsulant sheet of the third invention of the present application may contain components other than the polyolefin resin, the compound having two or more alkylperoxy groups represented by formula (1) in its structure, and triallyl isocyanurate, and the details and preferred forms of these components are also the same as those explained above regarding the first invention of the present application.
The preferred composition of the solar cell encapsulant sheet of the third invention of the present application, i.e., the preferred usage ratios of the polyolefin resin, the compound having two or more alkylperoxy groups represented by formula (1) in the structure, and triallyl isocyanurate, and other components used as desired, are the same as those described above for the first invention of the present application.

There is no particular limitation on the method for producing the solar cell encapsulant sheet of the third invention of the present application, but it is preferably produced by the production method of the first invention of the present application.
The solar cell encapsulant sheet of the third invention of the present application preferably consists of the crosslinkable resin composition of the second invention of the present application or contains the crosslinkable resin composition of the second invention of the present application.

The thickness of the solar cell encapsulant sheet of the third invention of the present application is not particularly limited, but is usually 0.01 to 2 mm, preferably 0.1 to 1.2 mm, and more preferably 0.2 to 0.9 mm. If the thickness is within this range, damage to the glass, solar cell element, thin-film electrode, etc. during the lamination process can be suppressed, and a high amount of photoelectric power generation can be obtained by ensuring sufficient light transmittance. Furthermore, it is preferable because the solar cell module can be laminated and molded at a relatively low temperature.

As a method for producing a solar cell module using the solar cell encapsulant sheet of the third invention of the present application, for example, the following method is preferable.
A laminate is formed by sandwiching a solar cell between solar cell encapsulant sheets, and the laminate is heated at 140° C. or higher and 200° C. or lower for 3 to 30 minutes while applying a pressure of 0.4 atm to 1 atm to the laminate to integrate them in an encapsulation process.

In the above-mentioned encapsulation step, the polyolefin resin constituting the solar cell encapsulant sheet is crosslinked and cured. That is, in the solar cell module manufactured in the above-mentioned step, the solar cell encapsulant sheet is a crosslinked and cured product, and has a different degree of crosslinking from the solar cell encapsulant sheet before the above-mentioned step, and the crosslinking agent and crosslinking assistant have been consumed in whole or in part.
The degree of crosslinking can be evaluated based on the gel fraction, and more specifically, it can be evaluated by, for example, the method described in the Examples of the present application.
The gel fraction is preferably 40% by mass or more, more preferably 45% by mass or more, and particularly preferably 50% by mass or more, based on the mass of the solar cell encapsulant sheet.

The laminate may be, for example, a front transparent protective member (e.g., a glass plate), a first solar cell encapsulant sheet, a solar cell, a second solar cell encapsulant sheet, and a back protective member (e.g., a back sheet laminated with various films) laminated in this order. The details of the configurations of the front transparent protective member, the solar cell, and the back protective member are widely known to those skilled in the art.

Solar cell modules manufactured using the solar cell encapsulant sheet of the third invention of this application effectively suppress problems such as air bubbles and swelling at high temperatures, and can be manufactured at low cost and with high productivity, making them usable in a wide range of applications, such as small solar cells such as those used in mobile devices and large solar cells installed on roofs and rooftops, and can be used in a variety of applications both indoors and outdoors.

The present invention will be specifically described below with reference to examples and comparative examples. Note that the present invention is not limited in any way by the following examples.

In the following Examples and Comparative Examples, the evaluation of each characteristic was carried out by the following methods.
(1) Impregnation Time 1 kg of polyolefin resin and a predetermined amount of a blended liquid, which is a liquid additive mixture containing a crosslinking agent, a crosslinking aid, and other additives, prepared by the method described below, were placed in a glass bottle, and impregnation was performed by rotating the glass bottle at about 170 rpm using a plate mix mill (PMM-20, manufactured by NS Koken Co., Ltd.) in an oven (PHH-401, manufactured by Espec Corporation) heated to 45°C.
The glass bottle was taken out of the oven at regular intervals and the state of the resin was observed. When it was confirmed that the surface of the resin and the wall of the bottle were not wet, it was determined that the impregnation was complete, and the time required up to that point was recorded as the impregnation time.
(2) Gel Fraction A sealing material sheet having a thickness of 400 μm×100 mm square was sandwiched between two PET films having a thickness of 50 μm×220 mm square, and the resultant was placed on a glass plate having a thickness of 3.2 mm×250 mm square. Using a laminator (LM-110×160, manufactured by NPC Corporation), the sealing material sheet was crosslinked and cured by first holding the sheet in a vacuum at 160° C. for 3 minutes and then heating and pressing the sheet at a pressure of about 1 atmosphere for a predetermined time.
About 1 g of a sample was taken from the above crosslinked and cured sealing material, and its weight was measured to an accuracy of four digits (this was defined as initial weight A).
The sample was placed in a heat-resistant bottle together with 100 ml of xylene, and then kept in an oven heated to 110° C. for 12 hours or more, after which it was filtered through a 30-mesh metal filter, and the sample remaining on the filter was transferred to a metal petri dish. The filtered sample on the metal petri dish was dried at 110° C. for 8 hours or more, and the weight of the sample after removing the xylene was measured (this was the post-drying weight B).
The gel fraction (%) was calculated from the initial weight A and the weight after drying B according to the following formula.
Gel fraction (%)=(weight after drying B (g)/initial weight A (g))×100
(3) High-Temperature Durability As shown in FIG. 3, a glass plate 31 having a thickness of 3.2 mm×75 mm×120 mm, a sealant sheet 32 having a thickness of 400 μm×75 mm×120 mm, an aluminum plate 33 having a thickness of 300 μm×50 mm square (simulating a solar cell), a cell fastening tape 35 (adhesive tape cut to a width of 9 mm×length of 25 mm), and a back sheet 34 having a thickness of 100 μm×75 mm×120 mm (manufactured by M.A. Packaging Co., Ltd., model name: PPN75S) were used, and the glass plate 31/sealant sheet 32/aluminum plate 33/cell fastening tape 35/sealant sheet 32/back sheet 34 were laminated in this order, and a laminator (LM-110×160, manufactured by NPC Co., Ltd.) was used to first hold the laminate in a vacuum at 160° C. for 3 minutes, and then perform a heating and pressurizing treatment at a pressure of about 1 atmosphere for a predetermined time, thereby producing a pseudo solar cell module sample. The cell fixing tape 35 was arranged so as to fix the four corners of the aluminum plate 33 .
After cooling the sample to room temperature, it was kept in an oven (PHH-401, manufactured by Espec Corporation) heated to 180° C. for 30 minutes and then removed, and the presence or absence of bulging of the backsheet 34 was judged by visual observation.

(Comparative Example 1)
The impregnation time was examined using an additive mixture containing 100 parts by mass of pellets of ethylene-α-olefin copolymer (Tafmer A-4070S, manufactured by Mitsui Chemicals, Inc., MFR: 3.6 g/10 min (190° C.), density: 870 kg/ ^m3 ) as a polyolefin resin, 0.6 parts by mass of t-butylperoxy 2-ethylhexyl carbonate (trade name: Luperox TBEC, manufactured by Arkema Yoshitomi Co., Ltd., purity: 97.7%) as a crosslinking agent, 0.8 parts by mass of triallylisocyanurate as a crosslinking aid, 0.3 parts by mass of 3-methacryloxypropyltrimethoxysilane (trade name: KBM503, manufactured by Shin-Etsu Chemical Co., Ltd.) as a silane coupling agent, 0.1 parts by mass of a light stabilizer, and 0.02 parts by mass of an antioxidant.
The results are shown in Table 1.

(Comparative Example 2)
Except for changing the amount of triallyl isocyanurate used as a crosslinking aid to 0.2 parts by mass, the impregnation time was examined in the same manner as in Comparative Example 1, and an encapsulant sheet was prepared with the same recipe, and the gel fraction and swelling at high temperatures were evaluated. The results are shown in Table 1.

Example 1
The impregnation time was examined in the same manner as in Comparative Example 2, except that 0.6 parts by mass of 2,5-dimethyl-2,5-di(t-butylperoxy)hexane (product name: Luperox 101, manufactured by Arkema Yoshitomi Co., Ltd., purity: 92.7%) was used instead of t-butylperoxy-2-ethylhexyl carbonate as the crosslinking agent, and an encapsulant sheet was prepared with the same recipe and evaluated for gel fraction and swelling at high temperature. The results are shown in Table 1.

Example 2
Except for changing the amount of 2,5-dimethyl-2,5-di(t-butylperoxy)hexane used as a crosslinking agent to 0.9 parts by mass, the impregnation time was examined in the same manner as in Example 1, and an encapsulant sheet was prepared with the same recipe, and the gel fraction and swelling at high temperatures were evaluated. The results are shown in Table 1.

Example 3
The impregnation time was examined in the same manner as in Example 2, except that 0.9 parts by mass of 1,1-di(t-butylperoxy)cyclohexane (product name: Luperox 331, manufactured by Arkema Yoshitomi Co., Ltd., purity: 79.6%) was used instead of 2,5-dimethyl-2,5-di(t-butylperoxy)hexane as the crosslinking agent, and an encapsulant sheet was prepared with the same recipe and evaluated for gel fraction and swelling at high temperature. The results are shown in Table 1.

With reference to Comparative Example 2 and each of the Examples, it is clear that by satisfying the requirements of the present invention, the generation of bubbles and the resulting swelling can be effectively suppressed even when used at high temperatures.
Furthermore, referring to Comparative Example 1 and each Example, it can be seen that by satisfying the requirements of the present invention, good impregnation of additives including a crosslinking agent and a crosslinking aid into a polyolefin resin is realized. This good impregnation enables melt kneading in a relatively short time using a standard extruder that does not have an injection nozzle installed between the supply port of the extruder and the tip of the screw, and can significantly improve the cost and productivity of the solar cell encapsulant sheet.

The solar cell encapsulant sheet of the present invention can effectively suppress problems such as the generation of air bubbles and swelling even when used at high temperatures in solar cell modules, and is also excellent in terms of cost and productivity, making it highly applicable in various industrial fields such as energy, electrical and electronics, architecture, construction, and machinery.

100: Extrusion molding machine
101: Supply port 103: Cylinder 105: Screw 107: Injection nozzle 109: Die 201: Container 203: Supply pump 31: Glass 32: Sealing material sheet 33: Aluminum plate 34: Back sheet 35: Cell stopper tape

Claims (10)

A step of preparing crosslinkable resin pellets by impregnating a crosslinking agent and a crosslinking assistant into pellets mainly composed of a polyolefin resin;
a step of feeding the crosslinkable resin pellets into a cylinder of an extrusion molding machine through a supply port thereof, and melt-kneading a resin composition containing the polyolefin resin, the crosslinking agent, and the crosslinking auxiliary in the cylinder;
extruding the resin composition into a sheet shape from a die of the extruder;
A method for producing a solar cell encapsulant sheet, comprising:
The crosslinking agent contains a compound having two or more alkylperoxy groups represented by the following formula (1) in the structure: R ¹ -OO- -(1)
(wherein R ¹ represents an alkyl group having 1 to 6 carbon atoms).
The crosslinking coagent comprises triallyl isocyanurate,
the compound having two or more alkylperoxy groups in its structure is blended in an amount of 0.4 to 1.5 parts by mass relative to 100 parts by mass of the polyolefin resin;
The above-mentioned production method, wherein the polyolefin resin is substantially free of structural units derived from vinyl acetate. The manufacturing method according to claim 1, wherein the time required for the step of producing the crosslinkable resin pellets is 100 minutes or less. The method according to claim 1 or 2, wherein the compound having two or more alkylperoxy groups in the structure has a structure in which the two or more alkylperoxy groups are bonded to the same carbon atom or are bonded via two or more carbon atoms. The manufacturing method according to any one of claims 1 to 3, which produces a solar cell encapsulant sheet having a gel fraction of 40% or more after encapsulating the solar cell. Polyolefin resin,
A compound having two or more alkylperoxy groups represented by the following formula (1) in its structure:
R ¹ -OO- -(1)
(wherein R ¹ represents an alkyl group having 1 to 6 carbon atoms), and triallyl isocyanurate,
the compound having two or more alkylperoxy groups is blended in an amount of 0.4 to 1.5 parts by mass relative to 100 parts by mass of the polyolefin resin;
The polyolefin resin is substantially free of structural units derived from vinyl acetate,
A crosslinkable resin composition for a solar cell encapsulant, comprising the triallyl isocyanurate in an amount of 0.4 parts by mass or less based on 100 parts by mass of the polyolefin resin. The crosslinkable resin composition according to claim 5, wherein the compound having two or more alkylperoxy groups in the structure has a structure in which the two or more alkylperoxy groups are bonded to the same carbon atom or bonded via two or more carbon atoms. Polyolefin resin,
A compound having two or more alkylperoxy groups represented by the following formula (1) in its structure:
R ¹ -OO- -(1)
(wherein R ¹ represents an alkyl group having 1 to 6 carbon atoms), and triallyl isocyanurate,
the compound having two or more alkylperoxy groups in its structure is blended in an amount of 0.4 to 1.5 parts by mass relative to 100 parts by mass of the polyolefin resin;
The polyolefin resin is substantially free of structural units derived from vinyl acetate,
The solar cell encapsulant sheet has a compounding amount of the triallyl isocyanurate of 0.4 parts by mass or less relative to 100 parts by mass of the polyolefin resin. The solar cell encapsulant sheet according to claim 7, wherein the compound having two or more alkylperoxy groups in the structure has a structure in which the two or more alkylperoxy groups are bonded to the same carbon atom or bonded via two or more carbon atoms. A solar cell module having a crosslinked and cured product of the solar cell encapsulant sheet according to claim 7 or 8. A step of encapsulating a solar cell with the solar cell encapsulant sheet according to claim 7 or 8, and a step of crosslinking and curing the solar cell encapsulant sheet.
The method for manufacturing a solar cell module comprising the steps of: