KR101721577B1 - Backsheet for solor cells having Polyvinylidene fluoride film - Google Patents

Abstract

The present invention relates to a backsheet for a solar cell laminated with a polyvinylidene fluoride film, and more particularly to a backsheet for a solar cell laminated with a polyvinylidene fluoride film. More particularly, the present invention relates to a composition for a polyvinylidene fluoride resin, a polymethyl methacrylate resin, To a backsheet for a solar cell, which is laminated on a substrate, and then the surface of the laminated fluororesin film is subjected to corona treatment at a specific strength. INDUSTRIAL APPLICABILITY The backsheet for a solar cell of the present invention is excellent in weatherability, heat resistance, dimensional stability, and adhesion to ethylene vinyl acetate as an encapsulating material, and thus can be usefully applied to the manufacture of solar cell modules.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a backsheet for solar cells having a polyvinylidene fluoride film laminated with a polyvinylidene fluoride film,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a back protection sheet for a solar cell laminated with a polyvinylidene fluoride (PVDF) film, wherein a PVDF film having a specific composition and surface roughness is laminated on a substrate, Is corona treated and has excellent adhesion with ethylene vinyl acetate as an encapsulating material.

In recent years, due to environmental pollution problems such as depletion of fossil energy sources and global warming due to carbon dioxide, securing clean alternative energy has become a global problem and attention is focused on solar cells.

Solar cells are made up of various materials and made up of modules, basically composed of glass, solar cell, encapsulant and backing sheet. The backside protection sheet fuses with the sealing material that fixes the cell at the rear side of the solar cell module, thereby protecting the module from physical impact, moisture and other contaminants from the external environment. Since solar cells are often installed outside on the basis of power generation characteristics, the backsheet must also have durability and weatherability to withstand long-term outdoor use. Accordingly, a fluororesin film excellent in durability and weather resistance has been most widely used as a film for a back protection sheet.

Polyvinyl fluoride (PVF) film, a trade name of Tedlar (DuPont), is generally used as a fluororesin for a backside protective sheet. Recently, in order to replace the PVF film and improve its function, other fluororesin films such as polyvinylidene fluoride (PVDF), chlorotrifluoroethylene-ethylene copolymer (ECTFE) and tetrafluoroethylene-ethylene copolymer (ETFE) And is widely used as a film material for a film.

Among them, PVDF resin can be melt-molded and can be used for various purposes because it has excellent weather resistance, corrosion resistance, chemical resistance and scratch resistance, and can be used for a long period of time. have.

US Pat. No. 4,226,904 discloses a polymethylmethacrylate (PMMA) film coated with a PVDF film. In order to improve the adhesion, PMMA is mixed with a dimethylformamide solvent, cast on a PVDF film, Evaporating the PVDF film layer, and pressing the PVDF film layer onto the PMMA resin layer. U.S. Patent No. 5,242,976 discloses a composition capable of adhering PVDF to a support by coextrusion, wherein the composition is a mixture of PMMA, PVDF, and acrylic elastomer. In addition, in order to solve the problem that the PVDF resin is incompatible with other resins other than the fluorine-based resin, Japanese Unexamined Patent Publication Nos. 55-044898 and 61-008350 and the like show excellent compatibility with the PVDF resin and other thermoplastic resins A PVDF / PMMA mixed layer is disposed between a three-layer extruded sheet in which a compatible PMMA resin is interposed between the vinyl chloride resin layer and an adhesive resin layer, a PVDF resin layer and a PMMA resin layer as an adhesive resin layer An extruded sheet improved in interlaminar adhesive strength and the like are interposed.

As can be seen from the prior art, since the PVDF film has weak adhesion to the support and the sealing material, it is necessary to mix the composition other than PVDF and the weather resistance, heat resistance and dimensional stability depend on the composition of the mixture. The mixed composition of the PVDF film laminated with the PVDF film should be well selected. In addition, it is usually required to maintain the adhesive strength of 60 N / 10 mm or more, although the adhesive strength to the backsheet and the sealing material for a solar cell is usually required to be 40 N / 10 mm or more. However, even if the adhesive strength is improved by mixing other compositions, the surface tension of the fluorine-based film itself is low, so that there is a limit in improving the adhesion with the sealing material.

Ethylene vinyl acetate (EVA) is widely used as an encapsulant. This encapsulant and adhesive property are one of the most important properties in the backsheet for solar cells.

Accordingly, the present inventors have continuously studied to develop a backsheet for a solar cell to which a polyvinylidene fluoride film having improved weatherability, heat resistance, scratch resistance and dimensional stability, and improved adhesion to ethylene vinyl acetate has been applied. As a result, after a polyvinylidene fluoride film having a specific composition containing polyvinylidene fluoride resin, polymethyl methacrylate resin and titanium dioxide and having a surface roughness controlled within a specific range was laminated on a substrate, Corona treatment with a specific strength results in meeting the above-mentioned object, thereby completing the present invention. Accordingly, it is an object of the present invention to provide a backsheet for a solar cell, which is excellent in weather resistance, heat resistance, scratch resistance, dimensional stability and adhesion to an encapsulant by using a fluororesin film.

The present invention relates to a resin composition comprising 50 to 90% by weight of a polyvinylidene fluoride resin; 5 to 25% by weight of polymethylmethacrylate resin; And titanium dioxide of 5-25% by weight; and containing a surface roughness of the base material to 0.3 ㎛ than polyvinylidene fluoride film On the other hand, or is laminated to both surfaces, the surface of the laminated film ^{60 ~ 120 W / m 2 ·} min Of the back surface protective sheet for a solar cell, which is corona-treated by corona discharge.

INDUSTRIAL APPLICABILITY The backsheet for solar cell of the present invention is excellent in weather resistance, heat resistance and dimensional stability by applying a polyvinylidene fluoride film having a specific composition and surface roughness, and is also excellent in ethylene vinyl acetate Adhesive property.

Hereinafter, the present invention will be described in detail.

The present invention relates to a resin composition comprising 50 to 90% by weight of a polyvinylidene fluoride resin; 5 to 25% by weight of polymethylmethacrylate resin; And titanium dioxide of 5-25% by weight; and containing a surface roughness of the base material to 0.3 ㎛ than polyvinylidene fluoride film On the other hand, or is laminated to both surfaces, the surface of the laminated film ^{60 ~ 120 W / m 2 ·} min The present invention relates to a backsheet for a solar cell, which is corona-treated by corona discharge.

The polyvinylidene fluoride resin may be a homopolymer or a copolymer of vinylidene fluoride. In the case of a copolymer, vinylidene fluoride and a comonomer are copolymerized in a weight ratio of 50:50 to 99: 1, and the comonomer is selected from vinyl fluoride, trifluoroethylene, chlorofluoroethylene, 1,2-difluoro (Alkyl vinyl ether), perfluoro (1,3-dioxol) and perfluoro (2,2-dimethyl-1,3-dioxol) ) Can be used. The content of the polyvinylidene fluoride resin in the polyvinylidene fluoride film of the present invention is preferably 50 to 90% by weight, and more preferably 60 to 80% by weight. When the content of the polyvinylidene fluoride resin is less than 50% by weight, it is difficult to obtain sufficient weather resistance, heat resistance, scratch resistance and dimensional stability required for the protective sheet film in the case of a solar cell, and if it exceeds 90% by weight, And there may be a problem of deterioration of adhesion with EVA.

The polymethyl methacrylate resin is used for increasing the adhesion of the film to EVA, and a homopolymer or copolymer of methyl methacrylate may be used. In the case of a copolymer, methyl methacrylate and a comonomer are copolymerized in a weight ratio of 50:50 to 99: 1, and the comonomer is selected from the group consisting of alkyl (meth) acrylate, acrylonitrile, butadiene, styrene and isoprene More than species can be used. The content of the polymethyl methacrylate resin in the film is preferably 5 to 25% by weight. When the content is less than 5% by weight, the adhesion to EVA may be deteriorated. When the content exceeds 25% by weight, the content of PVDF is relatively decreased, . ≪ / RTI >

The titanium dioxide is used for imparting UV resistance, whiteness, hiding degree, etc. to the film. The content of titanium dioxide in the film is preferably from 5 to 25% by weight. If the content of titanium dioxide is less than 5% by weight, there may be a problem of lowering the degree of concealment. If the content is more than 25% by weight, .

The backsheet for solar cell of the present invention is produced by laminating a polyvinylidene fluoride film having a surface roughness of 0.3 占 퐉 or less on the EVA adhesive side in order to improve the adhesive strength with EVA and further coating the surface of the film with a thickness of 60 to 120 W / Corona treatment with a corona dose of ² · min is a technical feature.

The above-mentioned substrate is not particularly limited as long as it is a film having barrier properties, but it may include at least one polyester film selected from polyethylene terephthalate, polyethylene naphthalate and polybutylene terephthalate; A film on which a metal is deposited; Metal foil or the like can be used. A polyvinylidene fluoride film may be laminated on one side or both sides of such a substrate to obtain a back side protective sheet suitable for the purpose of use.

The polyvinylidene fluoride film to be used at this time can control the surface roughness by placing the film on a roll heated at a surface temperature of 70 to 110 DEG C during extrusion and passing the film through a surface-treated squeezing roll with an opposite embossing treatment.

Further, the surface tension of the film is increased to 60 dynes or more through the corona treatment after the polyvinylidene fluoride film is laminated on the substrate, thereby improving the adhesion between the polyvinylidene fluoride film and EVA. When the corona treatment is performed, it is preferable to adjust the intensity of the corona doses in the range of 60 to 120 W / m ² · min. When the corona dose is 60 W / m ² · min , It may be difficult to obtain sufficient adhesive force with EVA even after the corona treatment. On the other hand, if it exceeds 120 W / m < ² > At this time, the definition of the coronado is expressed by the following equation (1).

[Equation 1]

Corona dose = P / (v · w · n)

Where P is the maximum power, v is the corona treatment speed, w is the width of the electrode, and n is the number of corona treated electrodes.

The back protection film for a solar cell laminated with a polyvinylidene fluoride film according to the present invention has excellent weather resistance, heat resistance, scratch resistance and dimensional stability, and particularly has a surface roughness of a specific roughness, The adhesive strength to ethylene vinyl acetate used as a material for a battery encapsulating material is excellent.

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

[Example]

Examples 1 to 3 and Comparative Examples 1 to 8

A mixture of vinylidene fluoride homopolymer (Solvay), a methyl methacrylate homopolymer (LGMMA) as a polymethyl methacrylate resin, and titanium dioxide (Huntsman) having a particle size of 230 nm was mixed with a polyvinylidene fluoride resin And melt-extruded to obtain a polyvinylidene fluoride (PVDF) film having a thickness of 25 탆. At this time, the surface roughness of the film was adjusted by passing through the embossed sieving roll. Thereafter, the PVDF film was laminated on a polyethylene terephthalate film (PET, SG00L 250 탆 SKC) as a substrate, and the surface of the PVDF film was corona treated (maximum power: 5 kw, electrode width: 1.5 m, Speed control) to obtain a backing sheet sample for a solar cell. The specific composition ratio, surface roughness, and corona dose of each example PVDF film are shown in Table 1 below.

division PVDF
(weight%) PMMA
(weight%) TiO ₂
(weight%) Surface roughness
(탆) Coronado
(W / m < ² > min) Example 1 80 10 10 0.29 80 Example 2 60 20 20 0.25 80 Example 3 80 10 10 0.29 60 Comparative Example 1 95 4 One 0.25 80 Comparative Example 2 40 30 30 0.22 80 Comparative Example 3 20 50 30 0.25 80 Comparative Example 4 80 10 10 0.47 80 Comparative Example 5 80 10 10 0.29 140 Comparative Example 6 80 10 10 0.29 40 Comparative Example 7 80 10 10 0.29 20 Comparative Example 8 80 10 10 0.29 0

Property measurement test

(1) Steel elongation

The strength and elongation were measured according to ASTM D882 to evaluate the durability of the sheet. The higher the strength, the better the durability.

(2) Heat shrinkage

To evaluate the heat resistance and dimensional stability of the sheet, a change in the length after heat treatment at 150 占 폚 for 30 minutes was confirmed. The lower the rate of change, the better.

(3)

In order to evaluate the heat resistance and weather resistance of the sheet, a pressure resistance test (PCT, pressure cooker test) was conducted to confirm the discoloration degree of the film. The pressure resistance test was carried out at 120 ° C and 1 atm for 75 hours, and the rate of yellow index (YI) change before and after the test was confirmed. The lower the rate of change, the better the heat resistance and weather resistance.

YI (%) = ((YI-PCT after YI) / PCT YI) * 100

division PVDF
(%) PMMA
(%) TiO ₂
(%) burglar
(kgf / mm ² ) Elongation
(%) Heat shrinkage
(%) △ YI
(%) Example 1 80 10 10 6.2 500 1.5 15 Example 2 60 20 20 5.2 330 0 25 Comparative Example 1 95 4 One 6.5 550 2 10 Comparative Example 2 40 30 30 2.5 80 6.5 75 Comparative Example 3 20 50 30 2.0 60 6 80

Table 2 shows the physical properties of PVDF, PMMA, and TiO 2 with varying contents. As shown in Comparative Examples 2 and 3, as the PVDF content is decreased, the strength is lowered and the heat shrinkage ratio and the vulcanization resistance are poor. In Comparative Example 1 containing an excessive amount of PVDF, there was no great problem in terms of weather resistance, heat resistance and dimensional stability. However, there was a problem that the titanium dioxide content was too low and the degree of concealment was low.

(4) Glossiness

And measured at an angle of 60 [deg.] (ASTM D523) using a gloss meter.

 (5) Surface tension

The surface tension was measured by using a Dyne Test Marker Pen (ASTM D-2578) (measuring surface tension of 30 to 60 dynes / cm on a measuring pen, and the membrane was destroyed for 3 seconds after the reagent was applied It is the standard when it is maintained without.)

(6) EVA adhesion

 An EVA (EF2N, SKC) sheet and a backsheet for solar cell were sequentially placed on a low iron tempered glass for solar cell and heated and fused in vacuum using a laminator. At this time, the EVA curing proceeded at a temperature of 150 DEG C for about 13 minutes. After one hour of heat fusion in the laminator, EVA adhesion was tested (180 ° peel test, 0.3 m / min)

division Surface roughness
(탆) Coronado
(W / m < ² > min) Glossiness
(%) Surface tension
(dyne) EVA adhesion
(N / 10 mm) Remarks Example 1 0.29 80 54 60 95 Example 3 0.29 60 54 60 62 Comparative Example 1 0.29 80 54 42 20 PVDF excess Comparative Example 4 0.47 80 10 60 45 Comparative Example 5 0.29 140 54 60 100 Comparative Example 6 0.29 40 54 60 40 Comparative Example 7 0.29 20 54 54 35 Comparative Example 8 0.29 0 54 30 10

Table 3 shows the results of the change of physical properties according to the surface roughness and the change of corona doses. In the case of Comparative Example 1, PVDF was added in an excessive amount to increase the fluorine content on the surface, and there was a problem that EVA adhesion was low even after the corona treatment. In Comparative Example 4 where the surface roughness was as high as 0.47 탆, the surface tension was good but there was a problem in the EVA adhesion. This is because the higher the surface roughness, the lower the efficiency of the corona treatment. However, the reason why the surface tension measurement is high is that the measurement reagent does not break the rough surface when the surface tension is measured with the polyphenol. Also, in Comparative Example 5 in which the film was subjected to corona treatment at a high corona dose, the EVA adhesion was not greatly improved even when the corona doses were increased, and the productivity was lowered under the same conditions. In the case of low corona doses, In the case of Comparative Examples 6 to 8 which were not conducted, the EVA adhesion was also lowered as the surface tension was lowered.

As a result, it was confirmed that the backsheet for a solar cell laminated with the polyvinylidene fluoride film of the present invention had excellent weather resistance, heat resistance, dimensional stability and EVA adhesion under specific composition and surface treatment conditions.

Claims (6)

A backsheet for a solar cell, which is adhered to an encapsulant made of ethylene vinyl acetate (EVA)
Wherein the back surface protective sheet is formed by laminating a polyvinylidene fluoride film on one side or both sides of a substrate, wherein one surface of the polyvinylidene fluoride film is coated with a thermoplastic resin having a thickness of 60 to 80 W / m ² min Corona treated with corona, directly bonded to an encapsulant of ethylene vinyl acetate (EVA)
Wherein the polyvinylidene fluoride film contains 60 to 80% by weight of a polyvinylidene fluoride resin, 10 to 20% by weight of a polymethyl methacrylate resin and 10 to 20% by weight of titanium dioxide, the surface tension of the film is 60 dyne And the surface roughness of the film has a value of 0.3 mu m or less,
A backsheet for a solar cell having an adhesive force of 62 to 95 N / 10 mm of a polyvinylidene fluoride film adhered to an encapsulating material of ethylene vinyl acetate (EVA).
The backsheet for a solar battery according to claim 1, wherein the polyvinylidene fluoride resin is a vinylidene fluoride homopolymer or a copolymer of vinylidene fluoride and a comonomer.
The process of claim 2 wherein said comonomer is selected from the group consisting of vinyl fluoride, trifluoroethylene, chlorofluoroethylene, 1,2-difluoroethylene, tetrafluoroethylene, hexafluoropropylene, perfluoro , Perfluoro (1,3-dioxole), and perfluoro (2,2-dimethyl-1,3-dioxole).
The backsheet for a solar cell according to claim 1, wherein the polymethyl methacrylate resin is a methyl methacrylate homopolymer or a copolymer of methyl methacrylate and a comonomer.
5. The backsheet for a solar cell according to claim 4, wherein the comonomer is at least one selected from the group consisting of alkyl (meth) acrylate, acrylonitrile, butadiene, styrene and isoprene.
The method of claim 1, wherein the substrate comprises at least one polyester film selected from the group consisting of polyethylene terephthalate, polyethylene naphthalate and polybutylene terephthalate; Or a film on which a metal is deposited; Or a metal foil.