JP5204375B2 - Polyester film for solar cell back surface protective film - Google Patents

Description

  The present invention relates to a polyester film used as a solar cell back surface protective film, that is, a polyester film for a solar cell back surface protective film.

  In recent years, a photovoltaic power generation system using a solar cell module has been spread as one of power generation means using clean energy. The structure of the solar cell module is generally such that a plurality of plate-like solar cell elements are sandwiched between a light receiving side glass substrate and a back side protective film, as described in, for example, Japanese Utility Model Laid-Open No. 6-38264. The internal gap is filled with sealing resin.

  A protective film is provided on the back surface of the solar cell module, and a polyester film having excellent mechanical properties, heat resistance, and moisture resistance is used for the protective film. For example, Japanese Patent Application Laid-Open Nos. 2002-26354 and 2003-60218 propose a solar cell back surface protective film using a polyethylene terephthalate film.

  As the solar cell back surface protective film, a white colored one may be used for the purpose of increasing the surface reflection of sunlight and increasing the power generation efficiency of the solar cell. In addition, in application to the architectural field where designability is important, not only white but also black or blue may be colored in accordance with the design of the building. In order to create the protective film colored in this way, a method of adding a colorant to the resin film constituting the protective film is known. Japanese Patent Application Laid-Open No. 2002-134771 describes a method of whitening a white pigment such as titanium oxide into a polyester film.

JP 2002-26354 A JP 2003-60218 A JP-A-60-250946 JP 2004-247390 A JP 2002-134771 A Japanese Utility Model Publication No. 6-38264

  However, when using a polyester film added with a colorant as a solar cell back surface protective film, the partial discharge start voltage may be low depending on the configuration, and sufficient insulation characteristics may not be obtained. When building, the problem of partial discharge cannot be ignored.

  The present invention provides a back surface of a solar cell having excellent mechanical properties, heat resistance, moisture resistance, and having excellent insulating properties capable of constructing a large-scale photovoltaic power generation system while having a high design property by containing a colorant. It is an object to provide a polyester film for a protective film.

That is, the present invention comprises a polyester composition containing 5 to 20 % by weight of a colorant, the surface of the colorant is treated with an affinity treatment agent, and the density of the film is 1. 45-1. 60 , a polyester film for a solar cell back surface protective film.

  According to the present invention, a solar having excellent mechanical properties, heat resistance, moisture resistance, and having excellent insulating properties capable of constructing a large-scale photovoltaic power generation system while having a high design property by containing a colorant. A polyester film for a battery back surface protective film can be provided.

  Hereinafter, the present invention will be described in detail.

[Polyester film]
The polyester film for solar cell back surface protective film of this invention consists of a polyester composition containing a coloring agent.
As the polyester of the polyester composition, a known aromatic polyester can be used. Aromatic dicarboxylic acid components such as terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, and ethylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol It is preferable to use an aromatic polyester composed of a glycol component such as 1,6-hexanediol. Of these, polyethylene terephthalate and polyethylene-2,6-naphthalenedicarboxylate are particularly preferred. The polyester may be a copolyester.

  The polyester composition contains a colorant. Content of a coloring agent is 0.5 to 50 weight% per 100 weight% of polyester compositions, Preferably it is 3 to 30 weight%, More preferably, it is 5 to 20 weight%. When the content of the colorant is less than 0.5%, in the case of white, the solar reflectance is low, and the effect of improving the power generation efficiency is small. On the other hand, if it exceeds 50% by weight, the film becomes brittle and practical mechanical strength cannot be obtained.

  As the white colorant, a white inorganic pigment is preferably used, and inorganic white pigments such as titanium dioxide, zinc oxide, zinc sulfide, and barium sulfate can be exemplified, and titanium dioxide is preferably used. As the colorant other than white, inorganic chromatic pigments can be used, for example, black pigments such as black iron oxide and carbon black, organic compounds such as azo, anthraquinone, phthalocyanine, thioindigo, quinacridone, and dioxazine. Dyes / pigments, bitumen, chrome vermilion, bengara and the like can be used.

The density of the polyester film of the present invention is 1.38 to 1.80, preferably 1.40 to 1.70 or less, more preferably 1.45 to 1.60. When the density is less than 1.38, the voltage at which partial discharge occurs is lowered, and the insulation characteristics are lowered. On the other hand, if the density exceeds 1.80, the film becomes brittle and practical mechanical strength cannot be obtained. In order to achieve this density, the colorant blended in the polyester composition is preferably one having a high density, preferably 3.0 g / cm ³ or more, more preferably 4.0 g / cm ³ or more.

As the colorant, a white colorant is typically used, but a colorant other than white may be used depending on the purpose of coloring.
Even when a high-density colorant is added, voids called voids are generated during the production of the film, and the film density may decrease. In the present invention, the void ratio of the film represented by the following formula is preferably 0 to 5%, more preferably 0 to 3%. If the void ratio exceeds 5%, the voltage at which partial discharge occurs is lowered and the insulation characteristics are lowered, which is not preferable.
Void ratio (%) = ((true density−actual density) / true density) × 100

  In order to obtain such a polyester film having a high density and a low void ratio, a colorant having a high affinity for polyester may be used. In particular, it is preferable to use a surface treatment agent having a high affinity for polyester on the surface of the colorant, that is, a colorant treated with an affinity treatment agent.

  Examples of the surface treatment agent for the colorant used for this purpose include oxides or hydrated oxides of metals such as aluminum, silicon, titanium, zirconium, tin, cerium, and bismuth, such as organic aluminum compounds, organic titanium compounds, and organic zirconium compounds. Examples of the organic metal compound include organic silicon compounds such as silane coupling agents and polysiloxanes, and phosphorus compounds such as aluminum phosphate and organic phosphate esters. Of these, aluminum, silicon, zirconium oxides or hydrous oxides, or organosilicon compounds are preferred.

  In addition to the colorant, the polyester film for a solar battery back surface protective film of the present invention may contain a lubricant within a range that does not impair the insulating properties for the purpose of improving handling properties. As the lubricant, inorganic fine particles and / or organic fine particles can be used. Examples of the inorganic fine particles include calcium carbonate, calcium oxide, aluminum oxide, kaolin, and silicon oxide fine particles. Examples of the organic fine particles include crosslinked acrylic resin particles, crosslinked polystyrene resin particles, urea resin particles, melamine resin particles, and crosslinked silicone resin particles. Of these, kaolin and silicon oxide are preferable, and lump particles of silicon oxide are particularly preferable.

[Ultraviolet absorber]
In order to improve the weather resistance of the film, the polyester film for solar cell back surface protective film of the present invention may contain an ultraviolet absorber. As an ultraviolet absorber, a compound having a large effective absorption coefficient in a small amount may be used. For example, 2,2′-p-phenylenebis (3,1-benzoxazin-4-one), 2,2 ′-( 4,4'-diphenylene) bis (3,1-benzoxazin-4-one) and 2,2 '-(2,6-naphthylene) bis (3,1-benzoxazin-4-one) it can.

[Production of film]
The polyester film for a solar cell back surface protective film of the present invention is obtained by melt-extruding a polyester composition containing a colorant in advance into a film shape, and cooling and solidifying it with a casting drum to form an unstretched film. Tg + 60) Stretched once or twice or more in the longitudinal direction in the longitudinal direction so that the total magnification is 2 to 5 times, and then stretched so that the magnification is 2 to 5 times in the width direction at Tg to (Tg + 60) ° C. If necessary, it can be obtained by further heat treatment at 180 ° C. to 255 ° C. for 1 to 60 seconds.

  At this time, in order to make it difficult for voids to be generated in the film, the longitudinal stretch ratio and the lateral stretch ratio of the film are set to a low ratio, preferably 2 to 4 times, more preferably 2 to 3.5 times. The stretching in the longitudinal direction and the transverse direction may be performed at the same time, and in this case, it may be performed using a simultaneous biaxial film forming machine.

  In order to enhance the dimensional stability during heating, a method of shrinking in the vertical direction in the heat treatment process as shown in JP-A-57-57628, or a film as shown in JP-A-1-275031 A method of relaxing heat treatment in a suspended state can be used. The thickness of the film obtained is preferably 25 to 300 μm, more preferably 30 to 250 μm.

[Easily adhesive coating]
In the present invention, an easy-adhesive coating may be applied to one side of the polyester film for the purpose of improving the adhesiveness with the sealing resin of the solar cell. This easy-adhesion coating has a coating film of (A) a polyester resin or acrylic resin having a glass transition point in the range of 20 to 100 ° C., or a mixture of these resins and polyvinyl alcohol in an amount of 0 to 90% by weight; ) It is preferably formed using a paint containing a solid content of 10 to 100% by weight of a crosslinking agent. Preferred examples of the crosslinking agent (B) include oxazoline group-containing polymers, urea-based resins, melamine-based resins, and epoxy-based resins, and oxazoline group-containing polymers are particularly preferable.

  For coating, a general known coating method can be used. More preferably, an aqueous liquid containing a film-forming component is applied to a stretchable polyester film, followed by drying, stretching, and heat treatment. It is preferable. The solid content concentration of the aqueous liquid is usually 30% by weight or less, preferably 10% by weight or less.

  The stretchable polyester film is an unstretched polyester film, a uniaxially stretched polyester film, or a biaxially stretched polyester film. Of these, a longitudinally stretched polyester film uniaxially stretched in the film extrusion direction (longitudinal direction) is particularly preferred.

  When applying an aqueous coating liquid to a film, as a pretreatment for improving the coating property, the film surface is subjected to physical treatment such as corona surface treatment, flame treatment, plasma treatment, etc., or chemically combined with the composition. It is preferable to use an inert surfactant in combination.

  When applying an aqueous liquid to a polyester film, it is preferable to carry out a normal coating process, that is, a biaxially stretched and heat-fixed polyester film in a process separated from the film manufacturing process, so that dust, dust, etc. are easily involved. Absent. From such a viewpoint, application in a clean atmosphere, that is, application in a film manufacturing process is preferable. And according to this application | coating, the adhesiveness to the polyester film of the resin film as a coating film further improves.

As the coating method, any known coating method can be applied. For example, a roll coating method, a gravure coating method, a roll brush method, a spray coating method, an air knife coating method, an impregnation method, and a curtain coating method can be used alone or in combination. The coating amount is, for example, 0.5 to 20 g, preferably 1 to 10 g per 1 m ² of the running film. The aqueous liquid is preferably used as an aqueous dispersion or emulsion. The coating may be formed only on one side of the film or on both sides as necessary.

  The stretchable polyester film coated with the aqueous liquid is guided to a drying step and a stretching treatment step as necessary. Such processing can be performed under conditions accumulated in the industry. As preferable conditions, the drying conditions are 90 to 130 ° C. × 2 to 10 seconds, the stretching temperature is 90 to 150 ° C., the stretching ratio is 3 to 5 times in the longitudinal direction, 3 to 5 times in the transverse direction, It is 1 to 3 times in the direction, and 180 to 250 ° C. × 2 to 60 seconds when heat-fixed. At this time, it is preferable that the thickness of a coating film is 0.01-1 micrometer.

[Configuration of back surface protection film]
The polyester film for solar cell back surface protective film of the present invention can be used as a solar cell back surface protective film, either alone or in combination of two or more. For example, it may be bonded to another transparent polyester film for the purpose of improving insulating properties, or may be used as a solar cell back surface protective film by bonding to a film made of a weather resistant resin such as polyvinyl fluoride for the purpose of improving weather resistance. Good.

When used as a solar cell back surface protective film, a water vapor barrier layer is preferably laminated for the purpose of imparting water vapor barrier properties. The solar cell back surface protective film having this configuration preferably has a water vapor transmission rate of 5 g / (m ² · 24 h) or less as measured according to JIS Z0208-73.

  As such a water vapor barrier layer, a film or foil having a water vapor barrier property can be used. Examples of the film include a polyvinylidene chloride film, a polyvinylidene chloride coated film, a polyvinylidene fluoride coated film, a silicon oxide deposited film, an aluminum oxide deposited film, and an aluminum deposited film, and the foil includes an aluminum foil and a copper foil. Can be illustrated.

  These films or foils have a structure in which the polyester film of the present invention is laminated on the opposite side of the EVA (ethylene vinyl acetate) adhesive surface, or another resin film is further laminated on the outer side and sandwiched between the films. It can be used in the form.

Hereinafter, the present invention will be further described by examples. Each characteristic value was measured by the following method.
(1) Intrinsic Viscosity The viscosity of a solution using an orthochlorophenol solvent was measured and determined at 35 ° C.

(2) Void ratio It calculated | required from the following formula.
Void ratio (%) = ((true density−actual density) / true density) × 100
The true density was calculated from the weight ratio using the polyester polymer density 1.4 and the colorant density. The actual density was measured using a density gradient tube of calcium nitrate aqueous solution at a temperature of 23 ° C.

(3) Partial discharge starting voltage A biaxially stretched polyethylene terephthalate film having a thickness of 12 microns provided with a thin film layer of silicon oxide having a thickness of 80 nm on one side is used as a gas barrier film, and the gas barrier film is sandwiched between two sample films. Then, using a polyurethane adhesive made by Takeda Pharmaceutical Co., Ltd. (main agent Takelac A515 / curing agent Takenate A50 = 10/1 solution), a protective film was prepared by pasting together using a dry laminating machine. The partial discharge start voltage (Umax) of this protective film was determined according to the partial discharge test of IEC60664-1 using a partial discharge tester (model KPD2050) manufactured by Kikusui Electronics Corporation. The measurement was carried out with 10 samples, and the average value was taken.

[Example 1]
Polyethylene terephthalate (inherent viscosity: 0.62) containing 10% by weight of white A (alumina-treated rutile type titanium oxide: JR-405, density 4.2, manufactured by Teika Co., Ltd.) as a colorant is maintained at 20 ° C. It was melt-extruded on the rotating cooling drum and made into an unstretched film. Subsequently, after extending | stretching 2.9 time at 100 degreeC to the vertical direction, the following coating agent A was apply | coated uniformly with the roll coater on the both surfaces. This coated film was subsequently dried at 95 ° C., stretched 3.2 times at 110 ° C. in the horizontal direction, and heat-set while shrinking 2% in the width direction at 230 ° C., and a solar cell back surface protective film having a thickness of 100 μm A polyester film was obtained. The thickness of the coating film was 0.08 μm.

<Coating agent A>
48 parts of dimethyl 2,6-naphthalenedicarboxylate, 14 parts of dimethyl isophthalate, 4 parts of dimethyl 5-sodiumsulfoisophthalate, 31 parts of ethylene glycol and 2 parts of diethylene glycol are charged into a reactor, and 0.05 part of tetrabutoxy titanium Was added and heated under a nitrogen atmosphere while controlling the temperature at 230 ° C., and the produced methanol was distilled off to conduct a transesterification reaction. Subsequently, the temperature of the reaction system was gradually raised to 255 ° C., and the pressure inside the system was reduced to 1 mmHg to carry out a polycondensation reaction to obtain a polyester. 25 parts of this polyester was dissolved in 75 parts of tetrahydrofuran, and 75 parts of water was dropped into the resulting solution under high-speed stirring at 10,000 rpm to obtain a milky white dispersion. Then, this dispersion was subjected to a reduced pressure of 20 mmHg. Distillation was performed, and tetrahydrofuran was distilled off to obtain an aqueous dispersion of polyester having a solid content of 25% by weight. Next, 3 parts of sodium lauryl sulfonate as a surfactant and 181 parts of ion-exchanged water are charged into a four-necked flask and the temperature is raised to 60 ° C. in a nitrogen stream, and then 0.5% ammonium persulfate is used as a polymerization initiator. Part, 0.2 part of sodium hydrogen nitrite is added, and further monomers 30.1 parts of methyl methacrylate, 21.9 parts of 2-isopropenyl-2-oxazoline, polyethylene oxide (n = 10) methacrylic acid A mixture of 39.4 parts and 8.6 parts of acrylamide was added dropwise over 3 hours while adjusting the liquid temperature to 60 to 70 ° C. After completion of dropping, the reaction was continued with stirring while maintaining the same temperature range for 2 hours, and then cooled to obtain an acrylic aqueous dispersion having a solid content of 35% by weight.

  On the other hand, 0.2% by weight of silica filler (average particle size: 100 nm) (trade name Snowtex ZL manufactured by Nissan Chemical Co., Ltd.), polyoxyethylene (n = 7) lauryl ether (Sanyo Chemical Co., Ltd.) as a wetting agent An aqueous solution containing 0.3% by weight of the trade name NAROACTY N-70) was prepared. Coating agent A was prepared by mixing 10 parts by weight of the above polyester aqueous dispersion, 5 parts by weight of the acrylic water dispersion and 85 parts by weight of the aqueous solution.

The obtained polyester film for solar cell back surface protective film had an actual density of 1.48 and a void ratio of 1.3%.
When the partial discharge start voltage was measured using this polyester film for solar cell back surface protective film, it was 960 V and the favorable insulation performance was shown.

[Examples 2 to 4 and Comparative Examples 1 to 4 ]
A polyester film having a thickness of 100 μm was obtained in the same manner as in Example 1 except that the type and amount of the colorant to be contained were changed as shown in Table 1. Table 1 shows the measurement results of the partial discharge start voltage.

  As is clear from the results of Table 1, the polyester film for the back surface protective film of the solar cell of the present invention showed good insulation performance.

[Example 5 ]
As a colorant, polyethylene-2,6-naphthalate (inherent viscosity: 0.58) containing 8% by weight of Colorant A was melt-extruded on a rotating cooling drum maintained at 60 ° C. to obtain an unstretched film. Subsequently, after extending | stretching 2.8 time at 140 degreeC to the vertical direction, the following coating agent A was apply | coated uniformly with the roll coater on the both surfaces. This coated film was subsequently dried at 150 ° C., stretched 3.1 times at 110 ° C. in the transverse direction, and heat-set while shrinking 2% in the width direction at 245 ° C., and a solar cell back surface protective film having a thickness of 100 μm A polyester film was obtained. The thickness of the coating film was 0.06 μm.

The actual density of the solar cell back surface protective film was 1.45, and the void ratio was 2.0%.
When the partial discharge start voltage was measured using this film for solar cell back surface protective film, it was 938V and showed favorable insulation performance.

  The polyester film for a solar cell back surface protective film of the present invention can be suitably used as a protective film for the back surface of a solar cell having excellent insulating properties capable of constructing a large-scale solar power generation system.

Claims (3)

It consists of a polyester composition containing 5 to 20 % by weight of a colorant, the surface of the colorant is treated with an affinity treatment agent, and the density of the film is 1. 45-1. The polyester film for solar cell back surface protective films characterized by being 60 .   The polyester film for solar cell back surface protective films of Claim 1 whose void ratio of a film is 0 to 5%. The solar cell back surface protective film which comprises the polyester film for solar cell back surface protective films of Claim 1 or 2 .