KR101747495B1

KR101747495B1 - Back sheet

Info

Publication number: KR101747495B1
Application number: KR1020140113042A
Authority: KR
Inventors: 권윤경; 김현철
Original assignee: 주식회사 엘지화학
Priority date: 2014-08-28
Filing date: 2014-08-28
Publication date: 2017-06-14
Also published as: KR20160025769A

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a back sheet and a photovoltaic module including the back sheet. In the back sheet according to the present application, a base film and a fluoropolymer film are attached through a pressure- This makes it possible to provide a photovoltaic module which is reusable due to the improvement and which is also excellent in long-term reliability.

Description

BACK SHEET {BACK SHEET}

The present application relates to a backsheet and a photovoltaic module comprising the same.

Recently, interest in renewable energy and clean energy has increased due to global environmental problems and depletion of fossil fuels. Among them, photovoltaic energy attracts attention as a representative pollution-free energy source that can solve environmental pollution problem and fossil fuel depletion problem. .

Photovoltaic (PV) solar photovoltaic (PV) technology is a device that converts sunlight into electric energy. Since it is required to be exposed to the external environment for a long time in order to easily absorb sunlight, various packaging for protecting the cell is performed, ), And these units are referred to as photovoltaic modules.

The photovoltaic module is required to include a back sheet having excellent properties such as weather resistance and durability so as to stably protect the photovoltaic cell even when exposed to the external environment for a long period of time. When the light is absorbed and converted into electric energy, shall.

On the other hand, Patent Document 1 proposes a technique of using a urethane-based adhesive for attaching a base film and a fluorine film to the back sheet.

However, since the urethane-based adhesive has a large amount of urethane bonds, not only the reliability is low but also the initial adhesive force is strong, the reworkability is lost and reusability is impossible, and the adhesive strength is deteriorated over time.

Patent Document 1: Korean Patent Publication No. 2011-0034665

The present application provides a backsheet and a photovoltaic module comprising the same.

The present application relates to backsheets.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a diagram schematically showing a cross section of a back sheet according to the present application. Fig.

In one example, as shown in Figure 1, the backsheet of the present application comprises a base film 20; A fluoropolymer film (40) formed on at least one side of the base film; And the fluororesin film 40 may be adhered to the base film 20 and the fluororesin film 40 by the adhesive layer 30.

The back sheet of the present application is excellent in reliability compared to the case of using a conventional urethane adhesive because the base film and the fluorine polymer film are adhered to the pressure sensitive adhesive layer, and the adhesiveness is stronger with time, Reusable, and long-term reliability.

The base film is not particularly limited and various materials known in the art can be used and can be appropriately selected depending on the required functions and applications.

Examples of the base film include a single sheet such as an acrylic film, a polyether film, a polyester film, a polyolefin film, a polyamide film, a polyurethane film, a polycarbonate film and a polyimide film, A laminated sheet of polymer films, or a pneumatic article, and a polyester film can be usually used, but the present invention is not limited thereto. Examples of the polyester film include at least one selected from the group consisting of a polyethylene terephthalate (PET) film, a polyethylene naphthalate (PEN) film, and a polycarbonate (PC) film , But is not limited thereto.

The thickness of the base film is not particularly limited, but may be within a range of, for example, 10 탆 to 500 탆, 25 탆 to 400 탆, or 50 탆 to 300 탆. By adjusting the thickness of the base film within the above-mentioned range, it is possible to improve the electrical insulating property, moisture barrier property, mechanical property, handling property and the like of the multilayer film. However, the thickness of the base film according to the embodiments of the present application is not limited to the above-mentioned range, and it can be appropriately adjusted as required.

In order to improve the adhesion of the surface layer described above, the base film is subjected to spark discharge treatment at a high frequency such as corona treatment or plasma treatment on one side or both sides thereof; Heat treatment; Flame treatment; Anchor treatment; Coupling agent treatment; Primer treatment or a gas phase Lewis acid (ex. BF _3), can be done by a surface treatment such as a chemical activation treatment with sulfuric acid or hot sodium hydroxide. The surface treatment method may be carried out by any well-known means generally used in this field.

In addition, the base film may be provided with an evaporation layer of an inorganic oxide on one side or both sides from the viewpoint of improving moisture barrier properties and the like. The kind of the inorganic oxide is not particularly limited, and any inorganic oxide may be employed as long as it has moisture barrier properties. For example, silicon oxide or aluminum oxide can be used. The method of forming the inorganic oxide vapor deposition layer on one side or both sides of the base film is not particularly limited and may be a vapor deposition method generally used in this field. When an inorganic oxide deposit layer is formed on one side or both sides of the base film, the above-described surface treatment may be performed on the deposition layer after forming an inorganic oxide deposit layer on the surface of the base film.

The fluoropolymer film may include a fluororesin. The back sheet includes a fluoropolymer film containing a fluororesin, so that the present application can have improved weather resistance and durability.

As the fluororesin, various resins containing fluorine atoms known in the art can be used. Examples of the fluororesin include vinylidene fluoride (VF), vinyl fluoride (VF), tetrafluoroethylene (TFE), hexafluoropropylene (HFP), and the like. Perfluoroethyl vinyl ether (PMVE, perfluoro (methylvinylether)), perfluoroethyl vinyl ether (PMVE), perfluoroethyl vinyl ether Perfluoro (ethyl vinyl ether), perfluoropropyl vinyl ether (PPVE), perfluorohexyl vinyl ether (PHVE), perfluoro-2,2-dimethyl-1,3-dioxole (PDD) Copolymers or mixtures thereof comprising at least one monomer selected from the group consisting of methylene-4-methyl-4-methyl-1,3-dioxolane (PMD) in polymerized form, Quot; The fluororesin is a homopolymer or copolymer comprising vinylidene fluoride (VDF) in polymerized form; Or a mixture comprising the same.

The type of the comonomer that can be contained in the form of the polymer in the copolymer is not particularly limited and includes, for example, tetrafluoroethylene (TFE), hexafluoropropylene (HFP), chlorotrifluoro But are not limited to, ethylene (CTFE), trifluoroethylene, hexafluoroisobutylene, perfluorobutyl ethylene, perfluoro (methylvinylether), and perfluoroethyl vinyl ether perfluorohexyl vinyl ether (PHVE), perfluoro-2,2-dimethyl-1,3-dioxole (PDD), and perfluoro-2 Methylene-4-methyl-1,3-dioxolane (PMD), and the like, and examples thereof include at least one of hexafluoropropylene and chlorotrifluoroethylene. However, But is not limited thereto.

In one example, the fluororesin may be a mixture of a homopolymer comprising vinylidene fluoride in polymerized form and a copolymer of vinylidene fluoride and hexafluoropropylene, or a mixture of vinylidene fluoride and chlorotrifluoro , A copolymer of ethylene and a copolymer of vinylidene fluoride and hexafluoropropylene.

The content of the comonomer contained in the copolymer is not particularly limited and may be, for example, about 0.5 to 50 wt%, 1 to 40 wt%, and 7 wt% based on the total weight of the copolymer % To 40 wt%, 10 wt% to 30 wt%, or 10 wt% to 20 wt%. By controlling the content of the comonomer in the above range, it is possible to further improve the adhesive force while ensuring the durability and weather resistance of the multilayer film.

The weight average molecular weight of the fluororesin contained in the fluoropolymer film may be from 50,000 to 100, and may be from 100,000 to 700,000, or from 300,000 to 50,000, but is not limited thereto. As used herein, the term " weight average molecular weight " is a conversion value of standard polystyrene measured by GPC (Gel Permeation Chromatograph). In the embodiments of the present application, by controlling the weight average molecular weight of the fluorine polymer within the above range, excellent solubility and other physical properties can be secured.

The fluoropolymer film may further include a (meth) acrylic polymer in addition to the fluororesin.

The acrylic polymer may be any polymer that can be used in the adhesive field without limitation, for example, polymethyl methacrylate (PMMA); A copolymer of methyl methacrylate and glycidyl methacrylate (MMA-GMA); A terpolymer of methyl methacrylate, glycidyl methacrylate and hydroxyethyl methacrylate (MMA-GMA-HEMA); Or copolymers of methyl methacrylate and cyclohexyl maleimide (MMA-CHMI), but are not limited thereto.

The content of the (meth) acrylic polymer is preferably 1 to 50% by weight, more preferably 5 to 30% by weight. If the content of the (meth) acryl-based polymer is less than 1% by weight, it may be difficult to ensure sufficient adhesion. If the content is more than 50% by weight, the fluoropolymer film may have poor weather resistance.

The weight ratio of the vinylidene fluoride polymer to the (meth) acrylic copolymer is preferably 9 to 7: 1 to 3, but is not limited thereto. For example, when the fluorine-based polymer film contains a vinylidene fluoride copolymer and polymethyl methacrylate, the weight ratio thereof is preferably 9 to 7: 1 to 3. When the fluorine-based polymer film contains a vinylidene fluoride copolymer and a copolymer of methyl methacrylate and glycidyl methacrylate, the weight ratio thereof is preferably 9 to 7: 1 to 3. When the fluorine-based polymer film contains a vinylidene fluoride copolymer and a ternary copolymer of methyl methacrylate, glycidyl methacrylate and hydroxyethyl methacrylate, the weight ratio thereof is 9 to 6: 0.5 To 2: 0.5 to 2. When the fluorine-based polymer film contains a copolymer of a vinylidene fluoride copolymer, methyl methacrylate and cyclohexylmaleimide, the weight ratio thereof is preferably 9 to 7: 1 to 3.

The glycidyl methacrylate and cyclohexyl maleimide are not included alone but are included in the form of a copolymer of methyl methacrylate and glycidyl methacrylate, a copolymer of methyl methacrylate and cyclohexyl maleimide In addition to these, methyl methacrylate and hydroxyethyl methacrylate copolymers, methyl methacrylate and acrylic acid copolymers, copolymers of methyl methacrylate and methacrylic acid, and the like may be further used.

In addition to the (meth) acrylic polymer, hydroxyethyl methacrylate, methacrylic acid, acrylic acid, and the like may be further used.

The fluorine-based polymer film may further include a pigment and / or a filler for improving the power generation efficiency of the solar cell and improving the physical properties of the back sheet for a photovoltaic module. Examples of the pigment and / or filler include titanium dioxide, Silica, alumina, calcium carbonate, barium sulfate, carbon black, metal oxide, and the like, and pigments for imparting black pigments and other colors such as carbon black can also be used.

The thickness of the fluorine-based polymer film may be in the range of 1 占 퐉 to 50 占 퐉, 2.5 占 퐉 to 45 占 퐉, or 5 占 퐉 to 40 占 퐉. By adjusting the thickness of the fluoropolymer film within the above-described range, it is possible to increase the light diffusing property and reduce the manufacturing cost.

In the back sheet of the present application, the above-described base film and the fluorine-based polymer film may be adhered by a pressure-sensitive adhesive layer. The pressure-sensitive adhesive layer may comprise, for example, a crosslinked pressure-sensitive adhesive polymer.

In one example, the tacky polymer may include a (meth) acrylic acid ester-based monomer polymerization unit and a crosslinkable monomer polymerization unit. As used herein, the term " monomeric polymerization unit " may refer to a form in which the monomer undergoes a polymerization reaction to form a skeleton of the polymer, for example, a main chain or a side chain.

The kind of the (meth) acrylate monomer is not particularly limited. In the present application, for example, alkyl (meth) acrylate can be used, specifically, an alkyl (meth) acrylate having an alkyl group having 1 to 14 carbon atoms, preferably 1 to 8 carbon atoms in view of controlling the adhesive force of the pressure- Methacrylate may be used. Examples of such monomers include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, (Meth) acrylate, sec-butyl (meth) acrylate, pentyl (meth) acrylate, 2- ethylhexyl , Isooctyl (meth) acrylate or isononyl (meth) acrylate, and one kind or a mixture of two or more kinds can be used.

The crosslinkable monomer means a compound which simultaneously contains both a copolymerizable functional group such as a carbon-carbon double bond in the molecule and a crosslinkable functional group. The crosslinkable monomer can impart a crosslinking functional group to an acrylic resin to provide a crosslinking point or control the reliability and adhesion of the pressure-sensitive adhesive layer under high temperature or high humidity conditions.

Examples of the crosslinkable monomer that can be used in the present application include a hydroxy group-containing monomer or a carboxyl group-containing monomer, which may be used alone or in combination. Examples of the hydroxy group-containing monomer include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 6-hydroxyhexyl (Meth) acrylate, 2-hydroxyethyleneglycol (meth) acrylate or 2-hydroxypropyleneglycol (meth) acrylate; Examples of the carboxyl group-containing monomer include acrylic acid, methacrylic acid, 2- (meth) acryloyloxyacetic acid, 3- (meth) acryloyloxypropyl acid, 4- (meth) acryloyloxybutyric acid, Butyric acid, itaconic acid, maleic acid, and the like.

In the present application, the pressure-sensitive adhesive polymer may include 70 to 99 parts by weight of a polymerization unit of a (meth) acrylic acid ester monomer and 0.1 to 30 parts by weight of a polymerization unit of a crosslinkable monomer. In the present specification, the unit " weight part " may mean a ratio of the weight between the respective components. By adjusting the ratio of the monomers contained in the tacky polymer to the above range, a more desirable level of adhesion can be ensured.

The pressure-sensitive adhesive polymer may further include a copolymerizable monomer in addition to the (meth) acrylic acid ester-based monomer unit and the crosslinkable monomer unit.

The copolymerizable monomer is not particularly limited as long as it is a copolymerizable monomer. For example, the copolymerizable monomer may include a monomeric polymerization unit capable of forming a homopolymer having a glass transition temperature of 0 ° C or higher.

When the glass transition temperature of a monomer is defined in this specification, its glass transition temperature can refer to the glass transition temperature of the homopolymer when the monomer is polymerized to form a homopolymer. Thus, for example, the term "monomer capable of forming a homopolymer having a glass transition temperature of 0 ° C or higher" may mean that the glass transition temperature of a homopolymer formed by polymerizing only monomers is 0 ° C or higher.

The glass transition temperature of the monomer capable of forming a homopolymer having a glass transition temperature of 0 ° C or higher may be 0 ° C or higher or 5 ° C or higher in another example and the upper limit of the glass transition temperature of the monomer is not particularly limited, 250 ° C, 200 ° C, 150 ° C, or 120 ° C.

But may include various types of copolymerizable monomers without particular limitation as long as the glass transition temperature has the above-mentioned range. For example, methacrylate, tertiary butyl acrylate, tert-butyl methacrylate Butyl acrylate, tert-butyl methacrylate, isobutyl methacrylate, normal-butyl methacrylate, 1-hexadecyl (meth) acrylate, (Meth) acrylates having a straight-chain or branched-chain alkyl group such as methyl methacrylate, n-propyl methacrylate or sec-butyl methacrylate, ; N-alkenylformamide having 2 to 20 carbon atoms, 2 to 16 carbon atoms, 2 to 12 carbon atoms, 2 to 8 carbon atoms, or an alkenyl group having 2 to 4 carbon atoms, such as N-vinylformamide; Acrylamide, N, N-diphenyl (meth) acrylamide, N- (n-dodecyl) (meth) acrylamide, N- (meth) acrylamide such as N, N-dimethyl acrylamide or N-hydroxyethyl acrylamide, N-alkyl (meth) acrylamide (Meth) acrylamide, N, N-dialkyl (meth) acrylamide or N, N-diaryl (meth) acrylamide; Alkoxyalkyl (meth) acrylates such as 2-methoxyethyl (meth) acrylate and the like; Dihydrodicyclopentadienyl acrylate, cyclohexyl (meth) acrylate, benzyl (meth) acrylate, cyclopropyl (meth) acrylate, acrylate, N-naphthyl acrylate, 2-phenoxyethyl (meth) acrylate, phenyl (meth) acrylate, Acrylate, 2-phenylethyl (meth) acrylate, isobornyl (meth) acrylate, dicyclopentanyl (meth) acrylate or (Meth) acrylate having a saturated or unsaturated cyclic hydrocarbon group or an aromatic group such as cyclohexyl (meth) acrylate and the like; Or styrene may be exemplified.

When the tacky polymer is a copolymerizable monomer and contains a monomer capable of forming a homopolymer having a glass transition temperature of 0 ° C or higher, it is preferable that the tacky polymer comprises 40 to 99 parts by weight of a polymerization unit of a (meth) acrylic acid ester monomer; 1 to 30 parts by weight of a crosslinkable monomer; And 10 to 60 parts by weight of monomeric polymerization units capable of forming a homopolymer having a glass transition temperature of 0 DEG C or higher. The pressure-sensitive adhesive polymer may further contain 45 to 80 parts by weight of a polymerization unit of a (meth) acrylic acid ester monomer so as to secure a desired level of adhesion; 5 parts by weight to 25 parts by weight of a crosslinkable monomer; And 10 to 50 parts by weight of monomeric polymerization units capable of forming a homopolymer having a glass transition temperature of 0 DEG C or higher.

The adhesive polymer may further include a crosslinkable monomer capable of imparting a crosslinkable functional group to the polymer, which functions to control adhesion and reliability of the pressure-sensitive adhesive by reacting with a crosslinking agent to be described later. Examples of such a crosslinkable monomer include a carboxyl group-containing monomer and a nitrogen-containing monomer. Examples of the carboxyl group-containing monomer include acrylic acid, methacrylic acid, 2- (meth) acryloyloxyacetic acid, 3- (meth) acryloyloxypropyl acid, 4- (meth) acryloyloxybutyric acid, Acrylic acid dimer, itaconic acid, maleic acid and maleic anhydride. Examples of the nitrogen-containing monomer include (meth) acrylamide, N-vinylpyrrolidone and N-vinylcaprolactam. It is not. In the present application, a mixture of one kind or more of the above can be used.

The crosslinkable monomer that may be further included may be included in the adhesive polymer in an amount ranging from 0.01 to 10 parts by weight based on 100 parts by weight of the (meth) acrylic acid ester monomer. If the content is less than 0.01 parts by weight, the reliability of the pressure-sensitive adhesive may be deteriorated. If the content is more than 10 parts by weight, the adhesive strength may be deteriorated.

In one example, the tacky polymer may have a weight average molecular weight of 100,000 or more, 300,000 or more, or 500,000 or more. The term "weight average molecular weight" as used in the present application means a value converted to standard polystyrene measured by GPC (Gel Permeation Chromatography). The upper limit of the weight average molecular weight of the pressure-sensitive adhesive polymer is not particularly limited, but may be, for example, 3,000,000, 2,500,000 or 200,000. The range of the weight average molecular weight of the pressure-sensitive adhesive polymer may be adjusted to the above-mentioned range, which may be advantageous for forming a pressure-sensitive adhesive layer having a desired level of adhesion.

The method for producing the adhesive polymer is not particularly limited and may be a method in which the monomer is mixed at an appropriate ratio and solution polymerization, photo polymerization, bulk polymerization, suspension polymerization, Or by emulsion polymerization. [0033] The term " polymer " If necessary in this process, suitable polymerization initiators or molecular weight regulators, chain transfer agents and the like may be used together.

The pressure-sensitive adhesive layer may further comprise a crosslinking agent capable of crosslinking the pressure-sensitive adhesive polymer. The crosslinking agent may be a crosslinking agent having at least two or more functional groups capable of reacting with the crosslinkable functional group contained in the adhesive polymer, 2 to 10, 2 to 8, 2 to 6, or 2 to 4 Crosslinking agents may be used. As such a cross-linking agent, an appropriate type may be selected and used from among conventional cross-linking agents such as an isocyanate cross-linking agent, an epoxy cross-linking agent, an aziridine cross-linking agent or a metal chelate cross-linking agent considering the kind of the cross-linkable functional group of the adhesive polymer.

Examples of the isocyanate crosslinking agent include diisocyanate compounds such as tolylene diisocyanate, xylene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, isoboron diisocyanate, tetramethylxylene diisocyanate, and naphthalene diisocyanate; And a reaction product of a polyol such as trimethylolpropane or an isocyanurate adduct of the above diisocyanate compound. Of these, xylene diisocyanate or hexamethylene diisocyanate can be preferably used. As the epoxy crosslinking agent Is preferably at least one selected from the group consisting of ethylene glycol diglycidyl ether, triglycidyl ether, trimethylolpropane triglycidyl ether, N, N, N ', N'- tetraglycidylethylenediamine and glycerin diglycidyl ether There is at least one selected from the group true can be exemplified.

As the aziridine crosslinking agent, N, N'-toluene-2,4-bis (1-aziridinecarboxamide), N, N'-diphenylmethane-4,4'- (2-methyl aziridine) or tri-1-aziridinyl phosphine oxide, and the like, but not limited thereto, and the metal chelate Examples of the crosslinking agent include compounds in which a polyvalent metal such as aluminum, iron, zinc, tin, titanium, antimony, magnesium, and / or vanadium is coordinated to acetylacetone or ethyl acetoacetate.

The cross-linking agent may be contained in a proportion of, for example, 0.01 to 5 parts by weight, 0.015 to 4 parts by weight, 0.02 to 3 parts by weight or 0.025 to 1 part by weight based on 100 parts by weight of the adhesive polymer have. The adhesive force of the pressure-sensitive adhesive layer can be maintained at a desired level by controlling the cross-linking agent to be included in the pressure-sensitive adhesive polymer within the above-mentioned range.

The thickness of the pressure-sensitive adhesive layer is not particularly limited, but may be within a range of, for example, 1 탆 to 100 탆, 2.5 탆 to 75 탆, or 5 탆 to 50 탆. The thickness of the pressure-sensitive adhesive layer can be controlled within the above-mentioned range to form a pressure-sensitive adhesive layer which secures more desired pressure-sensitive adhesive force.

In one example, the pressure-sensitive adhesive layer may satisfy the following expression (1).

[Equation 1]

X - Y > 0

In the above formula (1), X is a pressure-sensitive adhesive layer having a thickness of 1 cm x 10 cm cut out in the width direction of the pressure-sensitive adhesive layer and allowed to stand at 85 DEG C and 85% for 3000 hours. Then, the adhesive strength measured at a peeling angle of 180 DEG and a peeling speed of 0.3 m / And Y represents an initial adhesive strength measured at a peel angle of 180 degrees and a peel rate of 0.3 m / min for a specimen cut to a width of 1 cm x 10 cm in the pressure-sensitive adhesive layer.

The pressure-sensitive adhesive layer included in the back sheet of the present application satisfies the above-mentioned formula, so that the pressure-sensitive adhesive layer increases with time even under high temperature / high humidity conditions, so that the re-workability is excellent and the back sheet can be reused.

The pressure-sensitive adhesive layer may further include at least one additive selected from the group consisting of a coupling agent, a tackifier, a UV stabilizer, an antioxidant, a colorant, a reinforcing agent, a filler, a defoamer, a surfactant and a plasticizer, if necessary.

The backsheet of the present application may further include various functional layers known in the industry as needed in addition to the above-mentioned layers.

Examples of the functional layer include an adhesive layer or an insulating layer. The adhesive layer and the insulating layer may be sequentially formed on the other surface of the substrate layer when the reflective layer is formed on one surface of the substrate layer.

The adhesive layer or insulating layer may be formed in various ways known in the art. The insulating layer may be, for example, a layer composed of ethylene vinyl acetate (EVA) or low density linear polyethylene (LDPE). The layer composed of the ethylene vinyl acetate (EVA) or the low density linear polyethylene (LDPE) functions not only as an insulating layer but also an adhesive force of the encapsulant of the photovoltaic module to reduce the manufacturing cost, It is possible to simultaneously perform the function of maintaining excellent.

As described above, the back sheet of the present application comprises a base film; A fluoropolymer film formed on at least one side of the base film; And the fluoropolymer film are adhered to each other by the adhesive layer, so that they are superior in reliability compared with the case where they are adhered by the conventional adhesive form, and they are reusable because of their strong adhesive force as time goes by And the long-term reliability can also exhibit an excellent effect.

The present application also relates to photovoltaic modules.

In one example, the photovoltaic module comprises a front substrate; The above-described back sheet, and two or more photovoltaic cells which are disposed between the front substrate and the back sheet and are spaced apart from each other.

The specific types of the front substrate and the photovoltaic cell that can be used in the above are not particularly limited. For example, the front substrate may be a conventional plate glass; Or a transparent composite sheet obtained by laminating a glass, a fluororesin sheet, a weather-resistant film and a barrier film. The photovoltaic cell may be, for example, an active layer of the silicon wafer type or a thin film active layer formed by chemical vapor deposition . Also, the photovoltaic cell may be an n-type cell or a p-type cell, but is not limited thereto.

The back sheet according to the present invention is excellent in reliability by attaching a base film and a fluoropolymer film through a pressure-sensitive adhesive layer and can be reused because of its strong adhesive force over time, Can be provided.

Hereinafter, the present application will be described in more detail by way of examples according to the present application and comparative examples not complying with the present application, but the scope of the present application is not limited by the following embodiments.

The physical properties in the following examples and comparative examples were evaluated in the following manner.

1. Molecular weight measurement

The weight average molecular weight (Mw) was measured using GPC under the following conditions, and the measurement results were converted using standard polystyrene of Agilent system for the calibration curve.

Measuring instrument: Agilent GPC (Agilent 1200 series, U.S.)

Column: Two PL Mixed B connections

Column temperature: 40 ° C

Eluent: THF (Tetrahydrofuran)

Flow rate: 1.0 mL / min

Concentration: ~ 1 mg / mL (100 μL injection)

2. Evaluation of durability

The backsheet prepared in Examples and Comparative Examples was cut to a width of 1 cm x 10 cm to prepare specimens. Thereafter, immediately after the sample was prepared, the sample was allowed to stand at 85 ° C and 85% relative humidity for 1000 hours, 2000 hours, and 3000 hours, and the measured adhesion was evaluated according to the following criteria.

○: Adhesion increases with time.

X: Adhesion decreases with time.

&Lt; Preparation of sticky polymer >

Manufacturing example 1. Preparation of adhesive polymer (A1)

55 parts by weight of n-butyl acrylate (BA), 30 parts by weight of isobornyl acrylate (IBOA), and 2 parts by weight of 2-hydroxyethyl acrylate were added to a 1 L reactor equipped with a cooling device, 15 parts by weight of HEA were added. Subsequently, 100 parts by weight of ethyl acetate (EAc) was poured into a solvent, and nitrogen gas was purged for 60 minutes to remove oxygen. Then, while keeping the temperature at 60 ° C, 2,2'-azo And 0.04 parts by weight of bis-2,4- (dimethylvaleronitrile) (V-65) were added to initiate the reaction. Thereafter, the reaction product which had been reacted for about 5 hours was diluted with ethyl acetate (EAc) to prepare a sticky polymer (A1).

Manufacturing example 2 to Manufacturing example 3. Adhesive polymers (B1 and < C1 )

Adhesive polymers (A2 and A3) were prepared in the same manner as in Preparation Example 1, except that raw materials and additives used in polymerization of the adhesive polymer (A1) were controlled as shown in Table 1 in Production Example 1 .

Raw material EA V-65 BA EHA IBOA HEA MA VP Stickiness
polymer A1 55 - 30 15 - - 100 0.04 B1 - 50 30 15 - 5 100 0.04 C1 - 50 - 10 40 - 100 0.04 Content Unit: g
BA: n-butyl acrylate
EHA: 2-ethylhexyl acrylate
IBOA: isobornyl acrylate
HEA: 2-hydroxyethyl acrylate
MA: (meth) acrylate
VP: 1-vinyl-2-pyrrolidone
EA: ethyl acetate
V-65: 2,2'-azobis (2,4-dimethyl valeronitrile)

&Lt; Preparation of coating composition >

Manufacturing example 4, Preparation of Coating Composition (A2)

0.25 parts by weight of xylene diisocyanate (Takenate D110N, Mitsui Chemicals, Inc.) as a cross-linking agent was uniformly mixed with 100 parts by weight of the adhesive polymer (A1) prepared in Preparation Example 1 to prepare a coating composition (A2).

Manufacturing example 5. Preparation of coating composition (B2)

0.25 parts by weight of xylene diisocyanate (Takenate D110N, Mitsui Chemicals) as a crosslinking agent was uniformly mixed with 100 parts by weight of the adhesive polymer (B1) prepared in Preparation Example 2 to prepare a coating composition (B2).

Manufacturing example 6. Coating composition ( C2 )

0.25 parts by weight of xylene diisocyanate (Takenate D110N, Mitsui Chemicals, Inc.) as a cross-linking agent was uniformly mixed with 100 parts by weight of the adhesive polymer (C1) prepared in Production Example 3 to prepare a coating composition (C2).

< Back sheet And photovoltaic module &

Example One.

The prepared coating composition A2 was coated on both sides of a PET (poly (ethylene terephthalate)) film (thickness: 200 μm) and dried, and then a fluorinated polymer film (Poly Vinylidene Fluoride, FWIB, SKC) To prepare a back sheet.

Further, a plate glass (thickness: about 3 mm), an encapsulating material with a thickness of 500 mu m, a crystal silicon wafer photovoltaic cell, a sealing material with a thickness of 500 mu m and a back sheet manufactured in this way were laminated in this order. Min for 30 seconds to fabricate a photovoltaic module.

Example 2.

A backsheet and a photovoltaic module were prepared in the same manner as in Example 1, except that the coating composition (B2) prepared in Preparation Example 5 was used in place of the coating composition (A2) used in Example 1.

Example 3.

A backsheet and a photovoltaic module were prepared in the same manner as in Example 1 except that the coating composition (C2) prepared in Preparation Example 6 was used in place of the coating composition (A2) used in Example 1.

Comparative Example One.

A backsheet and a photovoltaic module were prepared in the same manner as in Example 1, except that a urethane-based adhesive (Liostar 7200, available from Toyo Ink Company) was used in place of the coating composition (A2) used in Example 1.

Comparative Example 2.

A backsheet and a photovoltaic module were prepared in the same manner as in Example 1, except that a urethane-based adhesive (Liostar 7500, available from Toyo Ink Company) was used instead of the coating composition (A2) used in Example 1.

The results of molecular weight and durability evaluations for the above Examples and Comparative Examples are shown in Table 1 below.

division Example Comparative Example One 2 3 One 2 Of the tacky polymer
Molecular weight (unit: million) 148 74 100 - - durability ○ ○ ○ Fail × Fail: Strong initial adhesion, not peeling, tearing film

20: base film
30: pressure-sensitive adhesive layer
40: Fluorine-based polymer film

Claims

A base film; And
A fluorinated polymer film formed on at least one surface of the base film,
Wherein the base film and the fluorine-based polymer film are attached by a pressure-sensitive adhesive layer, the pressure-sensitive adhesive layer comprises a pressure-sensitive adhesive polymer,
[Equation 1]
X - Y > 0
In the above formula (1), X is a pressure-sensitive adhesive layer having a thickness of 1 cm x 10 cm cut out in the width direction of the pressure-sensitive adhesive layer and allowed to stand at 85 DEG C and 85% for 3000 hours. Then, the adhesive strength measured at a peeling angle of 180 DEG and a peeling speed of 0.3 m / And Y represents an initial adhesive strength measured at a peel angle of 180 degrees and a peel rate of 0.3 m / min for a specimen cut to a width of 1 cm x 10 cm in the pressure-sensitive adhesive layer.

The back sheet for a photovoltaic module according to claim 1, wherein the tacky polymer comprises 70 to 99 parts by weight of a (meth) acrylic acid ester monomer and 1 to 30 parts by weight of a crosslinkable monomer.

The back sheet for a photovoltaic module according to claim 1, wherein the tacky polymer further comprises a monomer polymerization unit capable of forming a homopolymer having a glass transition temperature of 0 ° C or higher.

The back sheet for a photovoltaic module according to claim 3, wherein the monomer capable of forming a homopolymer having a glass transition temperature of 0 ° C or higher is alkyl (meth) acrylate having a branched chain or straight chain alkyl group.

The adhesive polymer according to claim 1, wherein the tacky polymer comprises 40 to 99 parts by weight of a polymerized unit of a (meth) acrylic acid ester monomer; 1 to 30 parts by weight of a crosslinkable monomer; And 10 to 60 parts by weight of a monomeric polymerized unit capable of forming a homopolymer having a glass transition temperature of 0 ° C or more.

The back sheet for a photovoltaic module according to claim 1, wherein the tacky polymer has a weight average molecular weight of 100,000 or more.

The back sheet for a photovoltaic module according to claim 1, further comprising a crosslinking agent for crosslinking the tacky polymer.

The backsheet for a photovoltaic module according to claim 7, wherein the crosslinking agent is at least one selected from the group consisting of an isocyanate compound, an epoxy compound, an aziridine compound and a metal chelate compound.

The back sheet for a photovoltaic module according to claim 7, which comprises 0.01 to 5 parts by weight of a crosslinking agent based on 100 parts by weight of the adhesive polymer.

delete

The substrate film according to claim 1, wherein the base film is at least one selected from the group consisting of an acrylic film, a polyether film, a polyester film, a polyolefin film, a polyamide film, a polyurethane film, a polycarbonate film, Back sheet for photovoltaic modules of more than two types.

The back sheet for a photovoltaic module according to claim 1, wherein the base film has a thickness of 1 to 500 μm.

The fluorine-based polymer film according to claim 1, wherein the fluorine-based polymer film is at least one selected from the group consisting of polyvinylidene fluoride (PVDF), hexafluoropropylene (HFP), chlorotrifluoroethylene (CTFE), tetrafluoroethylene (TFE) Perfluoroethyl vinyl ether (PPVE), perfluoroethyl vinyl ether (PEVE), perfluoromethyl vinyl ether (PMVE), perfluoro-2,2- Dimethyl-1,3-dioxole (PDD), and perfluoro-2-methylene-4-methyl-1,3-dioxolane (PMD).

The back sheet for a photovoltaic module according to claim 1, wherein the fluoropolymer film further comprises a (meth) acrylic polymer.

15. The method of claim 14, wherein the (meth) acrylic polymer is selected from the group consisting of polymethyl methacrylate; Copolymers of methyl methacrylate and glycidyl methacrylate; Terpolymers of methyl methacrylate, glycidyl methacrylate, and hydroxyethyl methacrylate; And a copolymer of methyl methacrylate and cyclohexyl maleimide.

The back sheet for a photovoltaic module according to claim 1, wherein the thickness of the fluorine-based polymer film is in the range of 1 탆 to 50 탆.

The back sheet for a photovoltaic module according to claim 1, wherein the thickness of the pressure-sensitive adhesive layer is in the range of 1 탆 to 100 탆.

A front substrate; A photovoltaic module comprising: a back sheet for a photovoltaic module according to claim 1; and at least two photovoltaic cells disposed between the front substrate and the back sheet and spaced apart from each other.