KR101069732B1 - Composition of fluoro urethane film for back sheet of solar cell device and method for preparing the same - Google Patents

Abstract

The present invention relates to a novel fluorinated urethane film, a method for manufacturing the same, and a use thereof as a backsheet for a solar cell, and more particularly, a method for producing a fluorinated urethane film and a sol form having excellent moisture-proof and UV-blocking effect, It relates to a use for use as a backsheet for a photovoltaic cell and a method for coating the backsheet of a photovoltaic cell using the same.

The plastic moisture-proof film of the present invention not only protects the internal elements by blocking ultraviolet rays without permeating water vapor in the air, but also the film itself is excellent in weather resistance and durability, so that the protective action can be stably maintained for a long time. It can be very usefully applied to various package films including sheets. In addition, since the film layer can be directly formed on the surface by the sol-cast (sol-cast) it can be used to simply coat the film at a low cost without a separate adhesive or extrusion process.

Fluorinated, urethane film, solar cell, back sheet, sol, sol-cast, moisture proof, weather resistance, ultraviolet

Description

Composition of fluoro urethane film for back sheet of solar cell device and method for preparing the same}

The present invention relates to a novel fluorinated urethane film, a method for manufacturing the same, and a use thereof as a backsheet for photovoltaic cells, and more particularly, a method for producing a fluorinated urethane film having excellent moisture-proof and UV-blocking effect and a sol form thereof, The present invention relates to a use for a backsheet for a photovoltaic cell and a method for coating the backsheet of a photovoltaic cell using the same.

In general, the backsheet of the solar cell is used to protect the solar cell element from moisture in the air and to protect the EVA layer used for sealing the cell from ultraviolet rays. Therefore, weather resistance should be ensured by using a material which does not cause degradation of the polymer due to sunlight. In order to exhibit excellent performance in this role, fluorine-based resins having excellent moisture resistance and relatively stable against ultraviolet rays have been mainly used, and recently, films of other materials having excellent moisture resistance have been proposed.

The solar cell back sheet is a protective sheet manufactured by lamination with PET using the above materials (see FIG. 1), and is usually manufactured by pressing (or laminating) PVF on both sides of a PET film using an adhesive layer, or by PEN or PVDF. It is known to manufacture by the method of crimping | bonding a film with an adhesive layer, and the like. PVF and PVdF among the lamination materials are used when the water repellency of the fluorine compound is used as the fluorine resin. However, all of the above methods are manufactured by compressing the fluorine-based film by applying an adhesive layer on both sides of PET, and should include two main steps: application of an adhesive layer and compression of a moisture proof layer. The moisture permeability of the solar cell backsheet manufactured by the above method should be designed so that moisture permeation of at least 60 g / m ² -day occurs based on 25 μm thickness. To this end, the adhesion between PET and the moisture barrier should be high and stable against climate change.

In addition, DuPont's PVF (Tedra), which is currently used as a back sheet for photovoltaic cells, is sold in the form of a film, but it is in short supply because it cannot catch up with the expansion of demand. In addition, a separate adhesive is required and the price is very expensive in the laminating process. There are disadvantages. PVDF films likewise require the additional process of producing the film separately and have the disadvantage of using adhesives. Therefore, the development of a film composition having a durability that does not require a separate extrusion equipment and at the same time does not use an adhesive when manufacturing a film is urgently required.

Accordingly, the present inventors have made efforts to develop a new polyurethane film composition, and as a result, the durable fluorine paint 4-fluorinated polyol is polymerized in the form of a sol using a butylacetic acid solvent in a sol form and fluorinated by adding a sunscreen or the like. The present invention was successfully completed by preparing a urethane film composition and confirming that it can be easily cured by coating it on a plastic film in sol form.

An object of the present invention is to provide a novel fluorinated urethane film composition, a method for producing the same, and a use thereof as a backsheet for a solar cell.

In order to achieve the above object, the present invention provides a fluorinated urethane film composition having a moisture-proof property that can be coated by casting in a sol state in which a 4-fluorinated polyol and an isocyanate are polymerized.

The present invention also provides a use of the fluorinated urethane film composition to coat the backsheet of a solar cell.

The 4-fluorinated polyol is a copolymer of tetrafluoroethylene, vinyl alcohol and vinyl acetate, and preferably has a hydroxyl value of 50 to 70 mgKOH / g. Isocyanates include hexamethylene diisocyanate (HDI), hexamethylene diisocyanate trimer (HDI trimer), isophoron diisocyanate (IPDI) and methylene bis (4-cyclohexyl isocyanate) [ methylene bis (4-cyclohexyl isocyanate), H12MDI] is preferably at least one selected from the group consisting of.

In addition, the present invention (1) a 4-fluorinated polyol dissolved in a solvent is mixed with titanium dioxide; (2) adding and stirring a dispersant and an antifoam and a defoaming agent; (3) adding a UV stabilizer and mixing; (4) mixing the isocyanates; And (5) adding a curing accelerator; It provides a method for producing the fluorinated urethane film composition consisting of steps.

In addition, the present invention provides a coating method for applying a fluorinated urethane film composition obtained in the form of a sol according to the production method on one side or both sides of the film.

Hereinafter, the present invention will be described in detail.

The present invention provides a fluorinated urethane film composition having moisture resistance in which a 4-fluorinated polyol and an isocyanate are polymerized. The film composition of the present invention can be applied by casting in a sol (sol) state can easily coat the back sheet of the photovoltaic cell.

The 4-fluorinated polyol is preferably a copolymer of tetrafluoroethylene, vinyl alcohol and vinyl acetate, and also has a hydroxyl value of 50 to 70 mgKOH / g. It is desirable to.

The isocyanates include hexamethylene diisocyanate (HDI), hexamethylene diisocyanate trimer (HDI trimer), isophoron diisocyanate (IPDI) and methylene bis (4-cyclohexyl isocyanate) [methylene It is preferably selected from the group consisting of bis (4-cyclohexyl isocyanate). In addition, the 4-fluorinated polyol and the isocyanate preferably have a compounding ratio of 0.5 to 1.5 equivalent ratio, and more preferably 0.9 to 1.1 equivalent ratio.

In addition, the present invention (1) a 4-fluorinated polyol dissolved in a solvent is mixed with titanium dioxide; (2) adding and stirring a dispersant and an antifoam and a defoaming agent; (3) adding a UV stabilizer and mixing; (4) mixing the isocyanates; And (5) adding a curing accelerator; It provides a method for producing the fluorinated urethane film composition consisting of steps.

In step (1), the 4-fluorinated polyol is preferably a copolymer of tetrafluoroethylene, vinyl alcohol, and vinyl acetate, and has a hydroxyl value of 50 to 70 mgKOH. Preference is given to using / g.

In the step (1), it is preferable to use butyl acetic acid as the solvent, and the titanium dioxide is preferably added in an amount of 0.1 to 1 wt% based on the 4-fluorinated polyol, and more preferably 0.25 to 0.5 wt%. desirable. In addition, in the step (3), the UV stabilizer is preferably added in an amount of 0.1 to 3% by weight, and separately mixed with the fluorinated polyol dissolved in the solvent. Further, in the step (4), the isocyanate is hexamethylene diisocyanate (HDI), hexamethylene diisocyanate trimer (HDI trimer), isophoron diisocyanate (IPDI) and methylene bis ( 4-cyclohexyl isocyanate) [methylene bis (4-cyclohexyl isocyanate), H12MDI] is preferably selected from the group consisting of. In addition, in the step (5), the curing accelerator is preferably used at a concentration of 0.01 to 0.2% by weight of dibutyltindilaurate or tinoctanate as a urethane reaction catalyst.

Specifically, the present invention prepares a two-component fluorinated polyurethane film composition using a 4-fluorinated polyol having four fluorine in one monomer and an isocyanate compound forming a crosslink through a urethane bond as a curing agent. Polyurethane of the 4-fluorinated polyol has a perfluoroalkyl chain and has a very low surface energy, and thus is applied as a surface treatment agent such as various water / oil repellent agents, antifouling agents, mold release agents, and non-adhesive coating agents. When the polyurethane is formed by bonding with isocyanate, the bonding strength with the adherend is increased. In addition, when the fluorinated polyol is crosslinked under various conditions while controlling the molar ratio with various isocyanates, a fluorinated polyurethane film exhibiting various characteristics can be obtained. Such a two-component sol may be made of a sheet having a structure of fluorinated polyurethane-PET-fluorinated polyurethane having excellent bonding to the surface of a PET film.

The fluorinated polyurethane is a polymer containing a urethane bond group (-NHCOO-) in a molecular chain, and is produced by a reaction between an isocyanate (-NCO) and a fluorinated alcohol (-OH).

R-NCO (isocyanate) + HO-R '(alcohol)-> R-NHCOO-R' (urethane)

Fluorinated polyurethanes can have various properties in combination with various types of isocyanates to introduce dispersibility and surface properties in their original properties. The hydroxyl group (-OH) in the molecular structure of the fluorinated polyol reacts with the isocyanate to give the urethane group an adhesive property, and the alkoxy group (-OR) in the fluorinated polyol imparts the ability to dissolve in a polar solvent, thereby sol-casting The application of the law becomes possible.

The fluorinated polyols used in the fluorine-based polyurethanes proposed in the present invention are prepared by copolymerization of tetrafluoroethylene, vinyl alcohol, and vinyl acetate containing four fluorides to form one hydroxyl group. (-OH) is a polymer in which one alkoxy group (-OR) is repeatedly copolymerized with tetrafluoroethylene and has a structure of a 4-fluorinated polyol having a hydroxyl value of 50 to 60 mg KOH / g (Formula 1) Has Isocyanates, which are curing agents that react to form fluorinated urethanes, areocyanates include hexamethylene diisocyanate (HDI), hexamethylene diisocyanate trimer (HDI trimer), isophoron diisocyanate (IPDI) and Methylene bis (4-cyclohexyl isocyanate, H12MDI), which isocyanates are used alone or in mixtures of two or three.

In the fluorinated polyurethane, in determining the ratio of the fluorinated polyol and the isocyanate curing agent, the ratio of the isocyanate group (-NCO) of the curing agent to the hydroxyl group (-OH) of the polyol is preferably adjusted to a molar ratio of 0.5 to 1.5. It is more preferable to adjust by 1 equivalent ratio. At this time, when the ratio of the isocyanate group (NCO) is high, the hardness of the film is high and easily broken. On the other hand, when the ratio of the isocyanate group (NCO) is low, the degree of polymerization is low and the strength of the film is low. Therefore, the equivalent molar ratio of 1: 1 is more preferable.

In addition, the present invention provides a coating method for applying a fluorinated urethane film composition obtained in the form of a sol according to the production method on one side or both sides of the film.

In the coating method of the fluorinated urethane film composition, the temperature is preferably cured by exposing the reaction time in the range of 50 to 150 ℃ for 10 to 30 minutes. The fluorinated urethane film composition is preferably applied in a thickness range of 20 to 150 μm when used in a back sheet of a photovoltaic cell, and the film may be a polyester film, an aluminum deposited film, a dual structure film of aluminum foil and polyester, or the like. It may include, and may also include all of their double, triple or multi-layered film. Or both of the coating on both or one or both sides of the film.

Specifically, the present invention is to produce a highly moisture-proof film by applying PET by the sol-cast method, the sol is prepared by using a titanium dioxide as a pigment, using a dispersing agent, a viscosity control agent, a leveling agent for reducing the viscosity as an additive do. In addition, a small amount of ultraviolet absorber is added to enhance ultraviolet stability. The white sol thus prepared is mixed with a curing agent in the ratio defined above and applied to the surface of PET. The white sol has excellent adhesion to PET and has properties of fluorine resin to form a film having excellent moisture resistance. In addition, due to the characteristics of the molecular structure of fluorinated polyols, the resistance to ultraviolet rays is stronger than that of general CH bonds, which delays aging of the film. Titanium dioxide is dispersed in a fluorinated urethane sol, and is applied to a polyester film (PET) to prevent aging of PET films. The efficiency of the photovoltaic cell can be improved by reflecting the light in the visible and ultraviolet regions from the battery layer with high efficiency. After the sol is cured in the form of a film on the PET film, the surface polarity is high due to the influence of the urethane group contained in the fluorinated urethane and the alkoxy group from the fluorinated polyol. Finally, it facilitates the manufacture of the back sheet of the solar cell.

As described above, the plastic moisture-proof film of the present invention can effectively protect the internal elements by blocking ultraviolet rays without permeating water vapor in the air, and also the film itself can be stably maintained for a long time due to enhanced weather resistance and durability. Therefore, it can be very usefully applied to various package films including the back sheet of the solar cell. In addition, since the film layer can be directly formed on the surface by the sol-cast (sol-cast) it can be used to simply coat the film at a low cost without a separate adhesive or extrusion process.

Indeed, the fluorinated polyols of the present invention can be crosslinked by isocyanates and applied directly to the PET film surface and exhibit sufficient adhesion, and the fluorine in the molecular structure enhances not only moisture resistance but also UV resistance. In addition, since the fluorinated polyol and the curing agent have the form of a solution in which butyl acetate is dissolved as a solvent, the coating property is stable and can be manufactured as a solar cell back sheet by solcasting, drying, and curing without the lamination process by thermocompression bonding. have.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples.

However, the following Examples and Comparative Examples are merely illustrative of the present invention, the contents of the present invention is not limited by the following Examples.

In the following Examples and Comparative Examples, the properties of adhesion, moisture resistance, reflectivity and gas permeability were evaluated in the following manner.

(1) adhesion

The adhesion was tested by the peel-off test of the cured coating film after application of the film onto the substrate.

(2) moisture proof

Moisture resistance measured the permeability of water vapor according to ASTM E-96-E-80.

(3) reflectivity

Reflectance of the visible region was measured using an ultraviolet-visible spectrometer.

(4) gas permeability

The gas permeability of the fluorinated polyurethane was measured for the most influential oxygen in the air according to ASTN D-3985.

Example 1 Preparation of Backsheets Using 4-Fluorinated Polyols and Hexamethylene Diisocyanate (HDI)

In the present invention, in order to manufacture a backsheet using 4-fluoride polyol and HDI, 30 kg of 4-weighted polyfluorinated polyol butylacetic acid solution in a 150L kettle equipped with a stirrer and a condenser is added with titanium dioxide (DuPont, R-902) 27g was added. 0.7 kg and 1.7 kg of the dispersant, the defoaming agent, and the defoaming agent were added thereto and stirred. To adjust the viscosity again, 8.1 kg of butylacetic acid was added and dispersed while passing through an In-line Mill with stirring. Separately, a 65-wt% 4-fluorinated polyol butylacetic acid solution, 0.2 kg of thickener, and 1.7 kg of UV stabilizer were added to a 50L kettle to dissolve well. The two dispersions were mixed and dispersion was completed in a high speed in-line mill. The above dispersion was performed at room temperature. The above-mentioned sol in which the pigment is dispersed is mixed with HDI so that the ratio of isocyanate and fluorinated polyol is OH / NCO = 0.5 to 1.5, and then 0.1% dibutyltindilaurate (DBTDL) is added and then stirred well. It was applied to the PET film and ETFE film with a thickness of 40 μm. Both sides of the PET film were sequentially coated, and the ETFE film was cured by applying only one side. After completion of the curing PET film performance evaluation as a solar cell backsheet, the fluorinated polyurethane film coated on ETFE was peeled off to measure the physical properties of the film. The fluorinated polyurethane film thus formed had a thickness of 30 μm.

FIG. 1 schematically shows the structure of a back sheet (crystal silicon system) of a general solar cell. The solar cell module has a laminated structure as shown in FIG. 1, and a back sheet that can be adhered to the back side requires various performances such as electrical insulation and adhesion to an encapsulant (EVA) as well as weather resistance and moisture resistance to withstand outdoor use for a long time. . Figure 2 schematically shows a cross section coated with the fluorinated urethane film of the present invention.

Example 2. Preparation of backsheet using 4-fluorinated polyol and hexamethylene diisocyanate trimer (HDI trimer)

A hexamethylene diisocyanate (HDI) was converted to a hexamethylene diisocyanate trimer (HDI trimer) in the same process as described in Example 1 to prepare a backsheet film of a solar cell, and performance evaluation and physical property evaluation were performed. It was.

Example 3. Preparation of backsheet using 4-fluorinated polyol and isophoron diisocyanate (IPDI)

A hexamethylene diisocyanate (HDI) was converted to isophoron diisocyanate (IPDI) in the same process as described in Example 1 to prepare a backsheet film of a solar cell, and performance evaluation and physical property evaluation were performed. Was carried out.

Example 3. Preparation of backsheet using 4-fluorinated polyol and methylene bis (4-cyclohexyl isocyanate) [methylene bis (4-cyclohexyl isocyanate), H12MDI]

In the same process as described in Example 1, the hexamethylene diisocyanate (HDI) was replaced with methylene bis (4-cyclohexyl isocyanate) [methylene bis (4-cyclohexyl isocyanate), H12MDI], and a back sheet film of a solar cell Was prepared, and the performance evaluation and the physical property evaluation were performed.

Comparative Example 1.

In order to compare with the above embodiments of the present invention, titanium dioxide is mixed with PVF in a ratio of the resin of Example 1 to titanium dioxide to prepare a 30 μm thick film using an extruder, and PET and a roll extruder ( The back sheet was prepared by lamination using a roll press, and the gas permeability and moisture permeability were measured using the non-laminated film. The results are as shown in Table 1 below.

Comparative Example 2

In order to compare with the above embodiments of the present invention, the gas permeability and moisture permeability were measured using a film not prepared with a back sheet using PVdF in the same manner as in Comparative Example 1. The results are as shown in Table 1 below. Therefore, the backsheet using the fluorinated urethane of the present invention has the same level of adhesion and permeability to moisture and oxygen as compared to PVF and PVdF, which are conventionally proposed materials, and has a high dispersion of pigment as an advantage of sol dispersion. Good reflectivity to In addition, the film can be easily formed by solcast, simplifying the complexity of dispersing the pigment, preparing the film, and laminating it again.

Measurement item Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Adhesiveness (Removal / Adhesion) 0/100 0/100 0/100 0/100 0/100 0/100 UV-VIS Reflectivity (%) 98.1 97.8 98.3 98.2 94.9 95.3 Moisture Permeability (g / m2-day) 60 59.1 58.3 56.5 62.3 61.2 Gas permeability
cc / 100in2-24hr-atm-mil 3.3 3.4 3.1 3.3 3.2 3.3

Figure 3 shows the results of the weather resistance by measuring the gloss retention rate for the fluorinated urethane film of the present invention, Figure 4 shows the results of the weathering test by performing a degradation test for the fluorinated urethane film of the present invention. Therefore, as the gloss retention is high, it is known that aging of the coating film does not proceed. As shown in FIG. 3, the fluorine paint has a longer life of 7 years and 20 years than the acrylic paint, respectively.

FIG. 1 schematically shows the structure of a back sheet (crystal silicon system) of a general solar cell.

Figure 2 schematically shows a cross section coated with the fluorinated urethane film of the present invention.

3 is a result of measuring the gloss retention rate for the fluorinated urethane film of the present invention to investigate the weather resistance.

4 is a result of examining the weather resistance by performing a deterioration test for the fluorinated urethane film of the present invention.

Claims (16)

In the fluorinated urethane film composition which polymerized 4-fluorinated polyol and isocyanate, The 4-fluorinated polyol is a copolymer of tetrafluoroethylene, vinyl alcohol and vinyl acetate, and has a hydroxyl value of 50 to 70 mgKOH / g, The isocyanate is isophoron diisocyanate (IPDI) or methylene bis (4-cyclohexyl isocyanate) [methylene bis (4-cyclohexyl isocyanate), H12MDI], The 4-fluorinated polyol and the isocyanate are fluorinated urethane film compositions having moisture resistance, characterized in that the mixing ratio can be coated in a sol (sol) state in a ratio of 0.5 to 1.5 equivalents. delete The method of claim 1, The fluorinated urethane film composition is a fluorinated urethane film composition, characterized in that used to coat the back sheet of the solar cell. delete delete delete (1) mixing a 4-fluorinated polyol dissolved in a solvent with titanium dioxide; (2) adding and stirring a dispersant and an antifoam and a defoaming agent; (3) adding a UV stabilizer and mixing; (4) mixing the isocyanates; And (5) adding a curing accelerator; In the method of producing a fluorinated urethane film composition of claim 1, In step (1), the 4-fluorinated polyol is a copolymer of tetrafluoroethylene, vinyl alcohol, and vinyl acetate, and has a hydroxyl value of 50 to 70 mgKOH / g, Isocyanate in step (4) is isophoron diisocyanate (IPDI) or methylene bis (4-cyclohexyl isocyanate) [methylene bis (4-cyclohexyl isocyanate), The 4-fluorinated polyol and the isocyanate are prepared by casting in a sol state to be coated at a compounding ratio of 0.5 to 1.5 equivalents. delete The method of claim 7, wherein Butyl acetate in the step (1) is used as a solvent, the production method characterized in that the titanium dioxide is added in a concentration of 0.1 to 1% by weight relative to the 4-fluorinated polyol sol. The method of claim 7, wherein In the step (3), the ultraviolet light stabilizer is mixed separately and added in a concentration of 0.1 to 3% by weight. delete The method of claim 7, wherein In the step (5), the curing accelerator is a dibutyltin dilaurate (dibutyltindilaurate) or tinoctanate (tinoctanate) in the manufacturing method, characterized in that using a concentration of 0.01 to 0.2% by weight as a urethane reaction catalyst. A coating method in which the fluorinated urethane film composition obtained in sol form according to the manufacturing method of claim 7 is applied to one or both sides of the film. The method of claim 13, Coating method characterized in that the curing by exposure for 10 to 30 minutes in the temperature range of 50 to 150 ℃. The method of claim 13, The film includes a polyester film, an aluminum deposited film, and a dual structure film of aluminum foil and polyester, the coating method comprising a solar cell back sheet. The method according to any one of claims 13 to 15, The fluorinated urethane film composition is a coating method, characterized in that applied in the range of 20 to 150 μm thick.

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