JP2012044088A - Polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester film for solar cell back sheet excellent in hydrolysis resistance and adhesion.SOLUTION: In a polyester film for solar cell back sheet including a first layer having polyester as a major component and a second layer having polyester as a major component set up adjacent to the first layer, these two layers are biaxially stretch-oriented to form a film having a thickness of 50 to 400 μm in which an intrinsic viscosity and a terminal carboxyl group concentration of each layer are adjusted.

Description

  The present invention relates to a polyester film for a solar battery backsheet.

  In recent years, solar cells have attracted attention as the next-generation energy source, and development is proceeding up to the building field for electric and electronic parts and larger ones. In particular, in the case of a solar cell used outdoors, the solar cell backsheet film used as one of the components is strongly required to have durability (particularly hydrolysis resistance) against the natural environment. Furthermore, such a solar cell back sheet is required to have high adhesion that does not peel off from the solar cell.

  Here, Patent Documents 1 and 2 describe polyester films having excellent hydrolysis resistance. However, there is a problem that the polyester films described in these are inferior in adhesion. On the other hand, the cited document 3 describes a polyester film having excellent adhesion. However, the polyester film described in the cited document 3 has a problem that it is inferior in hydrolysis resistance.

JP 2007-204538 A JP 2007-70430 A JP-A-9-208720

  The object of the present invention is to provide a polyester film for a solar battery back sheet that is excellent in both hydrolysis resistance and adhesion.

  Here, in order to impart hydrolysis resistance, it was considered that the amount of terminal carboxyl groups was reduced, but it was found that if the amount of terminal carboxyls was reduced, the adhesion was also lowered. Under such circumstances, as a result of investigation by the present inventors, the polyester film has a two-layer structure, one layer reduces the amount of terminal carboxy groups, and the other layer has a specific range of terminal carboxy group amounts and intrinsic viscosity. Furthermore, by adjusting the thickness of the whole film, it was found that a polyester film for a solar battery back sheet excellent in both hydrolysis resistance and adhesion was obtained, and the present invention was completed. Specifically, the object of the present invention has been achieved by the following means.

(1) A solar cell backsheet having a thickness of 50 to 400 μm, which is a biaxially oriented film provided with the following second layer adjacent to the first layer and the following second layer. Polyester film.
First layer: a main component is a polyester obtained by condensation polymerization of a dicarboxylic acid component mainly composed of terephthalic acid and a diol component mainly composed of ethylene glycol, and has an intrinsic viscosity (IV) of 0.55 to 0.95. And the terminal carboxyl group density | concentration is 20 eq / t or less.
Second layer: Main component is a polyester obtained by condensation polymerization of a dicarboxylic acid component mainly composed of terephthalic acid and a diol component mainly composed of ethylene glycol, and has an intrinsic viscosity (IV) of 0.65 to 0.95. The terminal carboxyl group concentration is 25 eq / t or more and less than 40 eq / t, and the thickness is 0.3 μm or more and less than 20 μm.
(2) The polyester film for solar cell backsheet according to (1), wherein the first layer is a polyester containing a compound derived from a titanium catalyst.
(3) The polyester film for solar cell backsheet according to (1) or (2), wherein the difference in melt viscosity between the first layer and the second layer is 1 to 100 Pa · s.
(4) The polyester film for a solar battery backsheet according to any one of (1) to (3), wherein the terminal carboxyl group concentration of the second layer is 25 eq / t or more and less than 38 eq / t. .
(5) The polyester film for solar battery backsheet according to any one of (1) to (4), wherein the second layer is subjected to corona treatment, flame treatment, or glow discharge treatment. .
(6) The degree of plane orientation of the first layer and the second layer is 0.16 to 0.18, respectively, according to any one of (1) to (5) Polyester film for solar battery backsheet.
(7) The polyester film for solar cell backsheet according to any one of (1) to (6), wherein the first layer contains a magnesium compound.
(8) The solar cell back according to any one of (1) to (7), wherein the first layer contains a pentavalent phosphate ester having no aromatic ring as a substituent. Polyester film for sheet.
(9) The first layer includes a compound derived from a titanium catalyst, and the titanium catalyst is an organic chelate titanium complex having an organic acid as a ligand, (1) to ( 8) The polyester film for solar battery backsheet according to any one of the above.
(10) The polyester film for solar cell backsheet according to any one of (1) to (9), wherein the melting point (Tm) of the polyester contained in the first layer is 245 to 260 ° C.
(11) The polyester film for solar cell backsheet according to any one of (1) to (10), wherein the thickness of the first layer is 0.3 to 20 μm.
(12) The polyester film for solar cell backsheet according to any one of (1) to (11), wherein the difference in intrinsic viscosity between the first layer and the second layer is 0.01 or more.
(13) A solar cell using the polyester film for solar cell back sheet according to any one of (1) to (12).

 According to the present invention, it is possible to provide a polyester film for a solar battery back sheet which is excellent in both hydrolysis resistance and adhesion.

FIG. 1 is a diagram showing an example of the solar cell of the present invention.

Hereinafter, the contents of the present invention will be described in detail. In the present specification, “to” is used to mean that the numerical values described before and after it are included as a lower limit value and an upper limit value.
The “main component” in the present invention means a component having the highest content ratio (weight), and usually 90% by weight or more is the component, and preferably 99% by weight or more is the component.

The polyester film for solar battery backsheet of the present invention is a film obtained by providing the following first layer and the following second layer adjacent to the first layer and biaxially stretching and having a thickness of 50. It is -400 micrometers.
First layer: a main component is a polyester obtained by condensation polymerization of a dicarboxylic acid component mainly composed of terephthalic acid and a diol component mainly composed of ethylene glycol, and has an intrinsic viscosity (IV) of 0.55 to 0.95. And the terminal carboxyl group density | concentration is 20 eq / t or less.
Second layer: Main component is a polyester obtained by condensation polymerization of a dicarboxylic acid component mainly composed of terephthalic acid and a diol component mainly composed of ethylene glycol, and has an intrinsic viscosity (IV) of 0.65 to 0.95. The terminal carboxyl group concentration is 25 eq / t or more and less than 40 eq / t, and the thickness is 1 μm or more and less than 20 μm.
Hereinafter, these details will be described.

  The polyester used in the present invention is mainly composed of a polyester obtained by condensation polymerization of a dicarboxylic acid component containing terephthalic acid as a main component and a diol component containing ethylene glycol as a main component. As a method for producing the polyester used in the present invention, a known method can be adopted without departing from the gist of the present invention. Preferably, the dicarboxylic acid component having terephthalic acid as a main component and a diol component having ethylene glycol as a main component are melt-polymerized for production. In particular, when a polyester resin having an intrinsic viscosity exceeding 0.60 is used in the present invention, it is preferable to obtain a polyester resin obtained by melt polymerization through a solid phase polymerization step. Solid-phase polymerization can be suitably performed by using polyester in small pieces such as pellets. The solid phase polymerization is usually performed at 150 to 250 ° C., more preferably 170 to 240 ° C., further preferably 190 to 230 ° C. for 1 to 50 hours, more preferably 5 to 40 hours, and further preferably 10 to 30 hours. Is preferable. The solid phase polymerization is preferably performed in a vacuum or a nitrogen stream. Since the polymerization can proceed at a low temperature by performing solid phase polymerization, a polyester resin having a low terminal carboxyl group can be obtained. Solid-phase polymerization may be carried out in a batch mode (a method in which a resin is placed in a container and stirred while applying heat for a predetermined time), or a continuous mode (a resin is placed in a heated cylinder and this is stirred). It may be carried out by a system in which the gas is passed through the cylinder while being kept flowing for a predetermined time while being heated, and sequentially fed out.

In the present invention, such a polyester is used to provide two layers, a first layer and a second layer. Usually, it is provided by melt film formation such as melt lamination or coextrusion. More specifically, the polyester film of the present invention can be produced, for example, by the following method. That is, polyester chips that have been dried or undried by a known method are supplied using a melt extrusion apparatus and heated to a temperature equal to or higher than the melting point of each polymer to melt. The molten polymer is then extruded from the die. The method of providing the first layer and the second layer may be a coextrusion method or a sequential method, but is preferably a coextrusion method. Thereafter, it is rapidly cooled and solidified on the rotary cooling drum so that the temperature is equal to or lower than the glass transition temperature to obtain a substantially amorphous unoriented sheet. In this case, in order to improve the flatness of the sheet, it is preferable to improve the adhesion between the sheet and the rotary cooling drum. In the present invention, an electrostatic application adhesion method and / or a liquid application adhesion method is preferably employed. Also in the melt extrusion step, in the present invention, the residence time of the polyester in the extruder in the extrusion step is shortened. When a single screw extruder is used, the raw material has a water content of 50 ppm or less in advance, preferably 30 ppm or less. In the case of using a twin screw extruder, a vent port is provided, and a method of maintaining a reduced pressure of 800 Pascals or less, preferably 300 Pascals or less, more preferably 200 Pascals or less is adopted.
The polyester film of the present invention is formed by biaxially stretching an unstretched film obtained by melt-forming polyester. An unstretched film can be obtained by a known method such as a simultaneous biaxial stretching method or a sequential biaxial stretching method. As the conditions in this case, the stretching temperature can be selected from the glass transition point of polyester (hereinafter sometimes abbreviated as Tg) to Tg + 100 ° C., and the final temperature range is usually from 80 to 170 ° C. It is preferable from the physical properties and productivity of the film obtained. The stretching ratio can be in the range of 1.6 to 5.0 for both the longitudinal direction and the width direction of the film. From the viewpoint of adjusting the plane orientation coefficient fn, the stretching ratio is 2. for both the longitudinal direction and the width direction of the film. It is preferable to adjust in the range of 5 to 4.0. The stretching speed is preferably 1000 to 200000% / min. Further, the film is heat-treated after stretching, but the film can be heat-treated continuously in a heat-treatment chamber connected to a tenter that extends in the width direction, or heated in another oven, or with a heating roll. As heat treatment conditions, a temperature range of 120 to 245 ° C. and a time range of 1 to 60 seconds is usually used. Relaxing treatment may be performed for the purpose of improving thermal dimensional stability in the width direction and the longitudinal direction during heat treatment.

  The thickness of the polyester film of the present invention is 50 to 400 μm, preferably 60 to 300 μm, and more preferably 75 to 250 μm. By setting it as such a range, the film | membrane intensity | strength and rigidity required for a solar cell backsheet, and the moisture barrier property required for protection of the cell of a solar cell are provided.

  The polyester film of the present invention has no specific haze range, but can be 5% or less, and more preferably 1% or less when the transparency of the film is required.

1st layer The 1st layer in the polyester film of this invention has the said polyester as a main component, intrinsic viscosity (IV) is 0.55-0.95, and terminal carboxyl group density | concentration is 20 eq / t or less. .
When the intrinsic viscosity is less than 0.55, the hydrolysis resistance is deteriorated, and when it exceeds 0.95, the film forming property is deteriorated. The intrinsic viscosity is preferably 0.60 to 0.90, and more preferably 0.65 to 0.85.
On the other hand, when the terminal carboxy group concentration exceeds 20 eq / t, the hydrolysis resistance deteriorates. The terminal carboxy group concentration is preferably 18 to 8 eq / t, and more preferably 17 to 10 eq / t.
Moreover, 245-260 degreeC is preferable and, as for melting | fusing point (Tm) of polyester contained in a 1st layer, 248-258 degreeC is more preferable. By setting it as 245 degreeC or more, hydrolysis resistance can be improved more. Moreover, since it is not necessary to raise the polymer temperature at the time of melt film formation unnecessarily by setting it as 260 degrees C or less, the thermal decomposition at the time of melt film formation is suppressed.

  The first layer usually contains a compound derived from a titanium-based catalyst. Here, the compound derived from the titanium-based catalyst refers to what is added as a catalyst for the polycondensation reaction during the production of the polyester, and the titanium element content is preferably 20 ppm or less with respect to the first layer, More preferably, it is 10 ppm or less, and a minimum is 1 ppm, for example, Preferably it is 2 ppm. If the content of the titanium compound is too large, a decomposition reaction is likely to occur during film production, the molecular weight of the polyester is lowered and the strength and heat resistance are inferior. Moreover, when used as a member of a solar cell, the weather resistance and hydrolysis resistance may be inferior. Moreover, when there is too little titanium element content, the productivity at the time of polyester raw material manufacture will be inferior, and the polyester raw material which reached the target polymerization degree may not be obtained. In addition, the polycondensation reaction rate becomes slow, resulting in an increase in the terminal carboxyl group concentration of the resulting polyester, which may result in poor weather resistance and hydrolysis resistance.

The compound derived from the titanium catalyst used as a catalyst in the present invention is preferably an organic chelate titanium complex having an organic acid as a ligand, and the Ti catalyst may be an oxide or hydroxide. Alkoxides, carboxylates, carbonates, oxalates, organic chelate titanium complexes, and halides. The Ti-based catalyst may be used in combination of two or more titanium compounds as long as the effects of the present invention are not impaired.
Examples of Ti-based catalysts include tetra-n-propyl titanate, tetra-i-propyl titanate, tetra-n-butyl titanate, tetra-n-butyl titanate tetramer, tetra-t-butyl titanate, tetracyclohexyl titanate, tetraphenyl Titanium alkoxide such as titanate and tetrabenzyl titanate, titanium oxide obtained by hydrolysis of titanium alkoxide, titanium-silicon or zirconium composite oxide obtained by hydrolysis of a mixture of titanium alkoxide and silicon alkoxide or zirconium alkoxide, titanium acetate , Titanium oxalate, potassium potassium oxalate, sodium oxalate, potassium titanate, sodium titanate, titanium titanate-aluminum hydroxide mixture, titanium chloride, titanium chloride-aluminum chloride Miniumu mixture, titanium acetylacetonate, an organic chelate titanium complex having an organic acid as a ligand, and the like.
Among the Ti-based catalysts, at least one organic chelate titanium complex having an organic acid as a ligand can be suitably used. Examples of the organic acid include citric acid, lactic acid, trimellitic acid, malic acid and the like. Among them, an organic chelate complex having citric acid or citrate as a ligand is preferable.
For example, when a chelate titanium complex having citric acid as a ligand is used, there is little generation of foreign matters such as fine particles, and a polyester resin having better polymerization activity and color tone than other titanium compounds can be obtained. Furthermore, even when using a citric acid chelate titanium complex, by adding it at the stage of the esterification reaction, a polyester resin having better polymerization activity and color tone and less terminal carboxyl groups can be obtained compared to the case where it is added after the esterification reaction. It is done. In this regard, the titanium catalyst also has a catalytic effect of the esterification reaction. By adding it at the esterification stage, the oligomer acid value at the end of the esterification reaction is lowered, and the subsequent polycondensation reaction is performed more efficiently. In addition, complexes with citric acid as a ligand are more resistant to hydrolysis than titanium alkoxides, etc., and do not hydrolyze in the esterification reaction process, while maintaining the original activity and catalyzing the esterification and polycondensation reactions It is estimated to function effectively as
In general, it is known that the greater the amount of terminal carboxyl groups, the worse the hydrolysis resistance. By reducing the amount of terminal carboxyl groups by the addition method of the present invention, improvement in hydrolysis resistance is expected. The
Examples of the citric acid chelate titanium complex are readily available as commercial products such as VERTEC AC-420 manufactured by Johnson Matthey.
The quantification of the element derived from the titanium catalyst in the film can be performed, for example, according to the description in paragraph No. 0056 of JP-A No. 2007-204538.

 In addition, it is preferable not to contain a metal compound other than the compound derived from the titanium catalyst, but in order to reduce the volume specific resistance at the time of melting in order to improve the productivity of the film, metals such as magnesium, calcium, lithium, manganese, etc. Can be added to the first layer, for example, at 100 ppm or less, preferably 60 ppm or less, and most preferably 50 ppm or less. The lower limit value is not particularly defined, but can be, for example, 5 ppm or more. Among these, it is more preferable that a magnesium compound is included. By including a magnesium compound, the film forming property tends to be further improved. Examples of the magnesium compound include magnesium salts such as magnesium oxide, magnesium hydroxide, magnesium alkoxide, magnesium acetate, and magnesium carbonate. Among these, magnesium acetate is most preferable from the viewpoint of solubility in ethylene glycol. The amount of magnesium compound added is preferably such that the Mg element conversion value is 50 ppm or more, more preferably 50 ppm or more and 100 ppm or less in order to impart high electrostatic applicability. The addition amount of the magnesium compound is preferably an amount that is in the range of 60 ppm to 90 ppm, more preferably 70 ppm to 80 ppm in terms of imparting electrostatic applicability.

The first layer also preferably contains a pentavalent phosphate ester having no aromatic ring as a substituent. By including such a compound, it becomes possible to more effectively suppress thermal decomposition due to the addition of a titanium-based catalyst. As an example of a pentavalent phosphate ester having no aromatic ring as a substituent, at least one pentavalent phosphate ester having no aromatic ring as a substituent can be used. Examples of the pentavalent phosphate ester in the present invention include trimethyl phosphate, triethyl phosphate, tri-n-butyl phosphate, trioctyl phosphate, tris phosphate (triethylene glycol), methyl acid phosphate, and phosphoric acid. Examples include ethyl acid, isopropyl acid phosphate, butyl acid phosphate, monobutyl phosphate, dibutyl phosphate, dioctyl phosphate, and triethylene glycol acid phosphate.
Among pentavalent phosphate esters, phosphate esters having a lower alkyl group having 2 or less carbon atoms as a substituent [(OR) ₃ —P═O; R = alkyl group having 1 or 2 carbon atoms] are preferable, Specifically, trimethyl phosphate and triethyl phosphate are particularly preferable. In particular, when a chelate titanium complex coordinated with citric acid or a salt thereof is used as the catalyst as the titanium compound, the pentavalent phosphate ester has better polymerization activity and color tone than the trivalent phosphate ester. Furthermore, in the case of adding a pentavalent phosphate having 2 or less carbon atoms, the balance of polymerization activity, color tone, and heat resistance can be particularly improved. As an addition amount of a phosphorus compound, the quantity from which P element conversion value becomes the range of 50-90 ppm is preferable. The amount of the phosphorus compound is more preferably 60 ppm to 80 ppm, and even more preferably 65 ppm to 75 ppm.

In particular, in the present invention, it is preferable to use a combination of the magnesium compound and a pentavalent phosphate ester having no aromatic ring as the substituent. By using in combination, it is possible to more effectively achieve both the electrostatic applicability required for film formation and the thermal stability during melt extrusion. In the esterification reaction step in the present invention, the value Z calculated from the following formula (i) is calculated from the following relational expression (ii) for the titanium compound as the catalyst component and the magnesium compound and phosphorus compound as the additive. ) Is preferably added and melt polymerized so as to satisfy. Here, the P content is the amount of phosphorus derived from the entire phosphorus compound including the pentavalent phosphate ester having no aromatic ring, and the Ti content is the amount of titanium derived from the entire Ti compound including the organic chelate titanium complex. It is. As described above, by selecting the combined use of the magnesium compound and the phosphorus compound in the catalyst system containing the titanium compound and controlling the addition timing and the addition ratio, while maintaining the catalyst activity of the titanium compound moderately high, yellow A color tone with less taste can be obtained, and heat resistance that hardly causes yellowing can be imparted even when exposed to high temperatures during polymerization reaction or subsequent film formation (during melting).
(I) Z = 5 × (P content [ppm] / P atomic weight) −2 × (Mg content [ppm] / Mg atomic weight) −4 × (Ti content [ppm] / Ti atomic weight)
(Ii) + 0 ≦ Z ≦ + 5.0
This is an index for quantitatively expressing the balance between the three because the phosphorus compound not only acts on titanium but also interacts with the magnesium compound.
The formula (i) expresses the amount of phosphorus that can act on titanium by excluding the phosphorus content that acts on magnesium from the total amount of phosphorus that can be reacted. When the value Z is positive, it can be said that there is an excess of phosphorus that inhibits titanium, and conversely, when it is negative, there is a shortage of phosphorus necessary to inhibit titanium. In the reaction, since each atom of Ti, Mg, and P is not equivalent, each mole number in the formula is weighted by multiplying by a valence.

 Moreover, antimony can also be contained as a metal component other than the catalyst for producing the polyester of the present invention in the case of using a method such as a master batch method for blending particles and various additives described later. However, in order to obtain the excellent hydrolysis resistance and weather resistance of the present invention, the content of antimony with respect to the whole film is preferably 30 ppm or less, more preferably 20 ppm or less as antimony metal. The metal compound here does not include particles to be blended in the polyester described later.

  The plane orientation degree of the first layer is preferably 0.16 to 0.18, and more preferably 0.165 to 0.175. By setting the degree of plane orientation to 0.16 or more, the hydrolysis resistance can be improved, and by setting it to 0.18 or less, the withstand voltage can be improved.

  The thickness of the first layer is preferably 0.3 to 20 μm, and more preferably 0.5 to 15 μm. By setting it as such thickness, adhesiveness is improved, without reducing the hydrolysis resistance of a film.

Second layer The second layer in the polyester film of the present invention contains the above polyester as a main component, has an intrinsic viscosity (IV) of 0.65 to 0.95, and a terminal carboxyl group concentration of 25 eq / t or more and 40 eq / is less than t.
When the intrinsic viscosity is less than 0.65, the hydrolysis resistance is deteriorated, and when it exceeds 0.95, the film forming property is deteriorated. The intrinsic viscosity is preferably 0.68 to 0.90, and more preferably 0.70 to 0.85.
On the other hand, when the terminal carboxy group concentration is less than 25 eq / t, the adhesion tends to deteriorate, and when it exceeds 45 eq / t, the hydrolysis resistance deteriorates. The terminal carboxy group concentration is preferably 25 eq / t or more and less than 38 eq / t, and more preferably 27 to 36 eq / t.
Moreover, 245-260 degreeC is preferable and, as for melting | fusing point (Tm) of polyester contained in a 2nd layer, 248-258 degreeC is more preferable. By setting it as 245 degreeC or more, hydrolysis resistance can be improved more. Moreover, since it is not necessary to raise the polymer temperature at the time of melt film formation unnecessarily by setting it as 260 degrees C or less, the thermal decomposition at the time of melt film formation is suppressed.

  In the present invention, the second layer is preferably subjected to corona treatment, flame treatment, or glow discharge treatment, and more preferably nitrogen corona treatment in consideration of economy. Only a single process may be used, but a synergistic effect may appear by superimposing a plurality of processes. By applying such treatment, surface treatment can remove substances attached to the film and bleed-out oligomers during film formation, and provide an anchor effect by forming fine irregularities on the film surface. Or a reactive group such as a carboxyl group, amino group, or imide group that increases the adhesive strength, or generates a radical with extremely high reactivity. Adhesion is greatly improved.

  In the corona discharge treatment, a material to be treated is sandwiched between a pair of electrodes in an atmospheric pressure state, an AC high voltage is applied between both electrodes to excite the corona discharge, and the surface of the material to be treated is exposed to a corona discharge. Thus, it is known as a technique for modifying the surface state of a material to be treated. For the corona treatment, a conventionally known method such as a self-discharge method, a DC discharge method, or an AC discharge method can be adopted. The discharge electrode 1 and the dielectric coating roll (treatment roll) are arranged with a fixed gap (usually 1 to 5 mm, preferably 1.5 to 3.5 mm) adjusted by an adjusting bolt. The surface on the electrode surface side of the substrate web is treated by bringing the substrate web into close contact with the dielectric coating roll, and performing discharge while passing it so as to provide an air gap between the treatment surface side and the electrode. Further, as a special processing method, it is possible to perform both-side simultaneous processing by passing a film through the center of the gap. Iron or aluminum is used for the roll core of the dielectric coating roll, and a dielectric material such as a resin such as silicone, hibaron, EPT, ceramic, glass, or the like is used. As the electrodes, (corrosion resistant) metals such as aluminum and stainless steel and ceramics are used. In addition, the shape of the electrode in this case is a string-like shape such as a wire, a plate-like shape having a rectangular cross section, a thin-plate-like shape, a plate-like shape having an R-processed tip, and its side surface A taper-shaped one, a combination thereof, and the like are known.

The corona discharge treatment is preferably performed so that the wetting tension is 45 to 60 dyne / cm. The intensity of the discharge treatment is suitably 10 to 50 W · min / m ² , and the treatment may be performed in the air, but it is preferably carried out in an inert gas atmosphere such as argon, helium, nitrogen, etc. CO, CO ₂ , O _2, or a mixed gas thereof can be used. In view of economy, it is particularly preferable to carry out in a nitrogen atmosphere. The atmosphere of the corona discharge treatment is preferably 5 to 40 ° C. and the relative humidity (RH) is 80% or less. When the corona discharge treatment is performed in the atmosphere, ozone and nitric oxide (NOx) are generated, which not only deteriorates the working environment but also oxidizes electrodes and rolls. From the viewpoint of preventing such inconvenience, it is preferable that the corona discharge treatment apparatus of the present invention is provided with an apparatus for quickly exhausting the ozone and nitrogen oxide.

For the flame treatment, a method of surface treatment using a clean burner frame treatment apparatus, a esseCI frame treatment apparatus, or the like is preferably used. Also in this processing method, it is necessary to run the front end of the frame processing parallel to the film at a high speed, as in other surface treatments.
The glow discharge treatment can generate active species higher than the corona discharge at a low pressure of about 0.001 to 0.01 Torr. However, since such plasma processing is performed in a vacuum system, continuous processing is difficult, and productivity is remarkably inferior, and the equipment itself becomes large. Therefore, microwave glow discharge plasma or the corona discharge is generated between the discharge electrode and the object to be processed at room temperature and atmospheric pressure, and the atmospheric pressure (usually 760 Torr) is generated by the strong electric field induced. A form in which plasma is generated is preferably used.

  The plane orientation degree of the second layer is preferably 0.16 to 0.18, and more preferably 0.165 to 0.175. By setting the degree of plane orientation to 0.16 or more, the hydrolysis resistance can be improved, and by setting it to 0.18 or less, the withstand voltage can be improved.

  The thickness of the second layer is preferably 49.7 to 398 μm, and more preferably 49 to 350 μm. By setting it as such thickness, the film | membrane intensity | strength and rigidity required for a solar cell backsheet, and the moisture barrier property required for protection of the cell of a solar cell are provided.

(Relationship between the first layer and the second layer)
In the present invention, the difference in intrinsic viscosity between the first layer and the second layer is preferably 0.01 or more, and more preferably 0.02 or more. By setting it as such a structure, the adhesive strength of the 1st and 2nd layer at the time of co-extrusion becomes favorable.
In the present invention, the difference in melt viscosity between the first layer and the second layer is preferably 1 to 100 Pa · s, and more preferably 5 to 80 Pa · s. By setting it to 1 Pa · s or more, the adhesion tends to be improved. By setting it to 100 Pa · s or less, it is possible to more effectively suppress the occurrence of curling after stretching.
As described above, the plane orientation degrees of the first layer and the second layer are each preferably 0.16 to 0.18, but the difference between the two is preferably within 0.01.

The first layer or second layer of the present invention, preferably in the second layer, may be added fine particles for easy slipping. Regarding the fine particles, the description in 0024 to 0033 of JP-A-2007-204538 can be referred to.
Further, the first layer or second layer of the present invention, preferably in the second layer, may be introduced polar groups such as sulfoisophthalic acid. By introducing such a polar group, adhesion can be improved. For details, JP-A-6-43617 can be referred to.

(Solar cell)
The solar cell of the present invention refers to a system that converts sunlight into electricity. An example of the structure is shown in FIG. That is, the front sheet layer 1, the filling adhesive resin layer 2, the solar cell element main part 3, the filling adhesive resin layer 4, and the back sheet layer 5 are the basic configuration from the side where sunlight enters. The polyester film of the present invention is used for the backsheet layer. Some of these solar cells are built into the roof of a house, installed in farm ponds, ranches, wastewater and sewage treatment facilities, volcanoes and hot spring areas, buildings and fences, and used in electronic parts. Some of the solar cell modules transmit light called daylighting type or see-through type and are used for soundproof walls such as windows, highways and railways. In the present invention, it can be a particularly flexible type.

 The solar cell in which the polyester film of the present invention is preferably used is not particularly limited, but for example, a single crystal silicon solar cell, a polycrystalline silicon solar cell, a single junction type, or an amorphous structure composed of a tandem structure type, etc. Silicon solar cells, III-V compound semiconductor solar cells such as gallium arsenide (GaAs) and indium phosphorus (InP), II-VI compound semiconductor solar cells such as cadmium tellurium (CdTe), copper / indium / selenium system ( So-called CIS-based), copper / indium / gallium / selenium-based (so-called CIGS-based), copper / indium / gallium / selenium / sulfur-based (so-called CIGS-based) I-III-VI group compound semiconductor solar cells, Examples include dye-sensitized solar cells and organic solar cells. Among these, in the present invention, the solar cell is composed of a copper / indium / selenium system (so-called CIS system), a copper / indium / gallium / selenium system (so-called CIGS system), a copper / indium / gallium / selenium / sulfur system. An I-III-VI group compound semiconductor solar cell such as (so-called CIGSS type) is preferable.

  The present invention will be described more specifically with reference to the following examples. The materials, amounts used, ratios, processing details, processing procedures, and the like shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below.

  Various measurement methods used in Examples of the present application are as follows.

(Measurement method of intrinsic viscosity (IV))
The value calculated by the following formula from the solution viscosity measured at 25 ° C. in orthochlorophenol was used.
ηsp / C = [η] + K [η] ² · C
Where ηsp = (solution viscosity / solvent viscosity) −1, C is the weight of dissolved polymer per 100 ml of solvent (g / 100 ml, usually 1.2), and K is the Huggins constant (assuming 0.343). is there. The solution viscosity and solvent viscosity were measured using an Ostwald viscometer. The unit is indicated by dl / g.

(Measurement method of terminal carboxy group concentration)
The amount of terminal carboxyl groups was measured by a so-called titration method. That is, the polyester was dissolved in benzyl alcohol, phenol red indicator was added, and titrated with a water / methanol / benzyl alcohol solution of sodium hydroxide. The unit is eq / t (equivalent / ton).

(Measuring method of melt viscosity)
The melt viscosity (Pa · s) of the A layer and the B layer was obtained by measuring the melt viscosity at 280 ° C. shear rate of 100 sec ⁻¹ by measurement according to JIS K 7199 using a capillary rheometer manufactured by Toyo Seiki.

(Measurement method of plane orientation)
The film refractive index was measured using an Abbe refractometer manufactured by Atago Co., Ltd., using a sodium lamp as the light source.
fn = (nMD + nTD) / 2−nZD (A)
In the above formula (A), nMD represents the refractive index in the machine direction of the biaxially oriented film, nTD represents the refractive index in the direction orthogonal to the machine direction, and nZD represents the refractive index in the film thickness direction.

(Measuring method of melting point (Tm) of polyester)
Tm (° C.) was determined by measurement according to JIS K7121.

(Hydrolysis resistance)
The film was aged in an atmosphere of 120 ° C. and 100% RH, and the elongation at break was measured as the mechanical properties of the film. The determination was made based on the time required for the retention of the breaking elongation before and after the aging treatment to be 50 (%).
Breaking elongation retention ratio = (breaking elongation before treatment−breaking elongation after treatment) ÷ breaking elongation before treatment × 100
○: Time for 50% is 90 hours or more Δ: Time for 50% is 75 hours or more and less than 90 hours ×: Time for 50% is less than 75 hours

(Lamination characteristics (adhesion))
When the reflective sheet annealed and the polyester film of the present invention were laminated, they were cut into 100 cm ² squares and placed on a flat plate, and the four-point lift was measured. This average value was defined as curl and determined as follows.
○: Curl is 0 mm or more and less than 2 mm Δ: Curl is 2 mm or more and less than 5 mm ×: Curl is 5 mm or more

(Film forming property)
The film forming property was evaluated according to the following criteria.
○: Discharge is stable during melt extrusion, and there is no film thickness variation or appearance abnormality Δ: Slight fluctuations in discharge are observed during melt extrusion, but there are no practical problems with fluctuations in film thickness and abnormal appearance.
X: Discharge fluctuations are observed during melt extrusion, and film thickness fluctuations and appearance abnormalities are practical problems.

(Reflectance)
The spectrophotometer U-3410 manufactured by Hitachi was used to measure the spectral reflectance with respect to the white standard plate. The light wavelength range was 300 to 900 nm, and the reflectance at 550 nm was a representative value.

(Withstand voltage)
The voltage resistance of the manufactured polyester film was evaluated according to the following criteria.
○: Withstand voltage of 1000V or more Δ: Withstand voltage of 600 or more and less than 1000V ×: Withstand voltage of less than 600V

(Heat-resistant)
The heat resistance of the produced polyester film was evaluated according to the following criteria.
○: Film MD and TD dimension change average value less than 0.1% by heat treatment at 150 ° C. for 30 minutes
Δ: Film MD and TD dimensional change due to heat treatment at 150 ° C. for 30 minutes 0.1% or more and less than 0.3% X: Film MD and TD dimensional change due to heat treatment at 150 ° C. for 30 minutes is 0. 3% or more

(Electrostatic application)
After drying the resin to a moisture content of 50 ppm or less, it was extruded from a die with a lip clearance of 4.5 mm and a width of 0.8 m under the condition of a resin temperature of 285 ° C. and cast to a temperature of 10 ° C. with a diameter of 1.5 m The film was cast on a roll (cooling roll), and a film was formed by an electrostatic application method at an applied voltage of 12 KV.
○: Capable of casting without entrainment air up to a film forming speed of 50 m / min or more
Δ: Can be cast without entrainment air entrainment up to 30 m / min or more and less than 50 m / min. ×: Air entrainment can be seen at less than 30 m / min.

(Measurement of haze)
According to JIS-K7105, the turbidity of the film was measured with an integrating sphere turbidimeter NDH-300A manufactured by Nippon Denshoku Industries Co., Ltd.

(Strength of film)
A 90 mm square test piece was prepared and cracked at 23 ° C. using a surface impact tester with a thermostatic chamber (Hydroshot) manufactured by Shimadzu Corporation under the conditions of a punching speed of 5 m / sec, a punching punch diameter of 13 mm, and a die diameter of 3 inches. The generated energy was measured.
An energy of less than 1 J was evaluated as x, a value of 1 or more and less than 2 J was evaluated as Δ, and a value of 2J or more was evaluated as ◯.

(Stretchability)
When the film was successively biaxially stretched, the thickness accuracy of the film exceeded 10 μm, x was 5 μm or more and 10 μm or less, and Δ was less than 5 μm.

(Manufacture of polyester)
[Reactant production step]
(1) Esterification reaction In a first esterification reactor, 4.7 tons of high-purity terephthalic acid and 1.8 tons of ethylene glycol are mixed over 90 minutes to form a slurry, and continuously at a flow rate of 3800 kg / h. It supplied to the 1st esterification reaction tank. Further, an ethylene glycol solution of a citrate chelate titanium complex (VERTEC AC-420, manufactured by Johnson Matthey) in which citric acid is coordinated to Ti metal is continuously supplied, and the average residence time is maintained at 250 ° C. in the reaction vessel with stirring. The reaction was carried out for about 4.3 hours. At this time, the citric acid chelate titanium complex was continuously added so that the amount of Ti added was 9 ppm in terms of element. At this time, the acid value of the obtained oligomer was 600 eq / ton.
This reaction product was transferred to a second esterification reaction vessel and reacted with stirring at a temperature in the reaction vessel of 250 ° C. and an average residence time of 1.2 hours to obtain an oligomer having an acid value of 200 eq / ton. The inside of the second esterification reaction tank is partitioned into three zones, and an ethylene glycol solution of magnesium acetate is continuously supplied from the second zone so that the amount of Mg added is 67 ppm in terms of element, From the third zone, an ethylene glycol solution of trimethyl phosphate was continuously supplied so that the added amount of P was 65 ppm in terms of element.
(2) Polycondensation reaction The esterification reaction product obtained above was continuously supplied to the first polycondensation reaction tank, with stirring, a reaction temperature of 270 ° C., and a pressure in the reaction tank of 2.67 × 10 ⁻³ MPa. (20 torr) and polycondensation was carried out with an average residence time of about 1.8 hours.
Further, the mixture was transferred to the second double condensation reaction tank, and while stirring in this reaction tank, the reaction tank temperature was 276 ° C., the reaction tank pressure was 6.67 × 10 ⁻⁴ MPa (5 torr), and the residence time was about 1.2 hours. The reaction (polycondensation) was performed under the conditions.
Subsequently, it was further transferred to the third triple condensation reaction tank. In this reaction tank, the temperature in the reaction tank was 278 ° C., the pressure in the reaction tank was 2.0 × 10 ⁻⁴ MPa (1.5 torr), and the residence time was 1.5 hours. The reaction product (polyethylene terephthalate; hereinafter referred to as PET) having an intrinsic viscosity of 0.63 dl / g and a terminal COOH group concentration of 22 equivalents / ton by reacting under conditions (polycondensation) and pelletizing (diameter 3 mm, length 4 mm) Is abbreviated as).

  In the above production method, the raw materials dicarboxylic acid, diol, catalyst and addition amount thereof, Mg compound addition amount, phosphorus compound addition amount and the like are changed as shown in Table 1, and the resins A to S shown in Table 1 are changed. Manufactured.

(3) Solid phase polymerization Among the polyester resins used in the examples of the present application, the specific resins listed in Table 1 were obtained through a solid phase polymerization step. The solid phase polymerization was performed on the pelletized polyester at 210 ° C. under vacuum (50 Pa) or under a nitrogen stream.
Resin A: The resin of IV = 0.63 obtained by the above polycondensation reaction was subjected to solid phase polymerization treatment at 210 ° C. for 18 hours under vacuum (50 Pa).
Resin B: Resin with IV = 0.50 was obtained by setting the residence time of the third condensation reaction tank of the polycondensation reaction to 0.3 hours.
Resin C: Resin with IV = 0.60 was obtained by setting the residence time of the above-mentioned polycondensation reaction in the third condensation reaction tank to 1.2 hours.
Resin D: The resin of IV = 0.63 obtained by the above polycondensation reaction was subjected to solid phase polymerization treatment at 210 ° C. for 9 hours under vacuum (50 Pa).
Resin E: The resin of IV = 0.63 obtained by the above polycondensation reaction was subjected to solid phase polymerization treatment at 210 ° C. for 27 hours under a nitrogen flow.
Resin F: The resin of IV = 0.63 obtained by the above polycondensation reaction was subjected to solid phase polymerization treatment at 210 ° C. for 42 hours under a nitrogen flow (50 Pa).
Resin G: The resin of IV = 0.63 obtained by the above polycondensation reaction was subjected to solid phase polymerization treatment at 210 ° C. for 60 hours under vacuum (50 Pa).
Resin H: Resin with IV = 0.63 obtained by changing the catalyst of the polycondensation reaction to Ge (55 ppm) was subjected to solid phase polymerization treatment at 210 ° C. for 22 hours under vacuum (50 Pa). .
Resin I: The polycondensation reaction catalyst was changed to Ge (55 ppm), and the residence time of the third triple condensation reaction tank was changed to 0.5 hour to obtain a resin with IV = 0.55.
Resin J: The polycondensation reaction catalyst was changed to Ge (55 ppm), and the residence time of the third triple condensation reaction tank was changed to 1.8 hours to obtain a resin with IV = 0.65.
Resin K: Resin J was subjected to solid state polymerization treatment at 210 ° C. for 16 hours under vacuum (50 Pa).
Resin L: Resin J was subjected to solid state polymerization treatment at 210 ° C. for 36 hours under vacuum (50 Pa).
Resin M: Resin J was subjected to solid state polymerization treatment at 210 ° C. for 55 hours under vacuum (50 Pa).
Resin N: Resin with IV = 0.63 obtained by changing the catalyst of the polycondensation reaction to Sb (150 ppm) was subjected to solid phase polymerization treatment at 210 ° C. for 12 hours under vacuum (50 Pa). .
Resin O: No Mg compound was added during the polycondensation reaction. Furthermore, the obtained resin was subjected to solid phase polymerization treatment at 210 ° C. for 16 hours under vacuum (50 Pa).
Resin P: No P compound was added during the polycondensation reaction. Further, the obtained resin was subjected to solid state polymerization treatment at 210 ° C. for 11 hours under vacuum (50 Pa).
Resin Q: 3 mol% of the acid component was changed to sulfoisophthalic acid during the polycondensation reaction, and the obtained resin with IV = 0.63 was subjected to solid phase polymerization treatment at 210 ° C. for 17 hours under vacuum (50 Pa). Was done.
Resin R: During the polycondensation reaction, 6 mol% of the acid component was changed to sulfoisophthalic acid, and the resulting IV = 0.63 resin was subjected to solid-state polymerization at 210 ° C. for 17 hours under vacuum (50 Pa). Was done.
Resin S: The catalyst of resin R was changed to Sb, and the obtained resin with IV = 0.63 was subjected to solid phase polymerization treatment at 210 ° C. for 11 hours under vacuum (50 Pa).

(Production of a polyester film in which the first layer and the second layer are laminated)
(1) Co-extrusion After drying the polyester resin to a moisture content of 50 ppm or less, the first layer resin was put into a hopper of a uniaxial kneading extruder having a diameter of 150 mm, and the condition was 285 ° C. under a N ₂ stream. The second layer resin is put into a hopper of a single screw kneading extruder with a diameter of 30 mm, melted at 285 ° C. under a N ₂ stream, and a two-type two-layer or two-type three-layer structure using a feed block. The unstretched film was extruded at a speed of 10 m / min. After passing this melt (melt) through a gear pump and a filter (pore diameter: 10 μm), it was extruded from a die having a width of 0.8 m under the following conditions, and the temperature was adjusted to 10 ° C. and the diameter was 1.5 m. Cast on a cast roll (cooling roll).
(2) Stretching The unstretched film extruded and solidified on the cooling roll by the above method was sequentially biaxially stretched by the following method to obtain films having the thicknesses shown in the following table. The stretching was performed in the order of longitudinal stretching at 95 ° C. and transverse stretching at 140 ° C. in the order of longitudinal stretching and transverse stretching. Thereafter, the film was heat-fixed at 210 ° C. for 10 seconds and then relaxed by 3% in the lateral direction at 205 ° C. After stretching, both ends were trimmed by 10 cm, and after thicknessing was applied to both ends, a corona discharge treatment was performed, and 3000 m was wound around a resin core having a diameter of 30 cm. The width was 1.5 m and the winding length was 2000 m. Films having different thicknesses were obtained by adjusting the film forming speed of the unstretched film under the condition of a constant discharge amount.

<Stretching method>
(A) Longitudinal stretching The unstretched film was passed between two pairs of nip rolls having different peripheral speeds and stretched in the longitudinal direction (conveying direction). The preheating temperature was 90 ° C., the stretching temperature was 90 ° C., the stretching ratio was 3.5 times, and the stretching speed was 3000% / second.
(B) Transverse stretching The longitudinally stretched film was stretched laterally under the following conditions using a tenter.
<Condition>
・ Preheating temperature: 95 ℃
-Stretching temperature: 95 ° C
-Stretching ratio: 3.9 times-Stretching speed: 70% / second (3) Heat setting and thermal relaxation After transverse stretching, the film was heat-fixed at 210 ° C for 10 seconds and then relaxed by 3% in the transverse direction at 205 ° C.
(4) Winding After stretching, both ends were trimmed by 10 cm, and after the thickness was processed at both ends, 3000 m was wound around a resin core having a diameter of 30 cm. The width was 1.5 m and the winding length was 2000 m.

  In Table 1 above, the catalyst column indicates the type of metal and the amount of metal added (element-converted value). Further, the Mg compound and the phosphorus compound are shown in element equivalent amounts of magnesium and phosphorus, respectively.

DESCRIPTION OF SYMBOLS 1 Front sheet layer 2 Filling adhesive resin layer 3 Main part of solar cell element 4 Filling adhesive resin layer 5 Back sheet layer

Claims (13)

A polyester film for a solar battery back sheet, which is a film obtained by providing the following first layer and the following second layer adjacent to the first layer and biaxially stretching and orientation, and having a thickness of 50 to 400 μm.
First layer: a main component is a polyester obtained by condensation polymerization of a dicarboxylic acid component mainly composed of terephthalic acid and a diol component mainly composed of ethylene glycol, and has an intrinsic viscosity (IV) of 0.55 to 0.95. And the terminal carboxyl group density | concentration is 20 eq / t or less.
Second layer: Main component is a polyester obtained by condensation polymerization of a dicarboxylic acid component mainly composed of terephthalic acid and a diol component mainly composed of ethylene glycol, and has an intrinsic viscosity (IV) of 0.65 to 0.95. The terminal carboxyl group concentration is 25 eq / t or more and less than 40 eq / t, and the thickness is 0.3 μm or more and less than 20 μm. The polyester film for a solar battery backsheet according to claim 1, wherein the first layer is a polyester containing a compound derived from a titanium-based catalyst. The difference in melt viscosity between the first layer and the second layer is 1 to 100 Pa · s, and the polyester film for a solar battery backsheet according to claim 1 or 2. The terminal carboxyl group concentration of a 2nd layer is 25 eq / t or more and less than 38 eq / t, The polyester film for solar cell backsheets of any one of Claims 1-3 characterized by the above-mentioned. The polyester film for solar cell backsheet according to any one of claims 1 to 4, wherein the second layer is subjected to corona treatment, flame treatment, or glow discharge treatment. 6. The solar cell backsheet according to claim 1, wherein the first layer and the second layer have a plane orientation degree of 0.16 to 0.18, respectively. Polyester film. The polyester film for solar cell backsheet according to any one of claims 1 to 6, wherein the first layer contains a magnesium compound. The polyester film for solar cell backsheet according to any one of claims 1 to 7, wherein the first layer contains a pentavalent phosphate ester having no aromatic ring as a substituent. The first layer includes a compound derived from a titanium-based catalyst, and the titanium-based catalyst is an organic chelate titanium complex having an organic acid as a ligand. The polyester film for solar cell backsheets of 1. The polyester film for solar battery backsheet according to any one of claims 1 to 9, wherein the melting point (Tm) of the polyester contained in the first layer is 245 to 260 ° C. The polyester film for solar cell backsheets according to any one of claims 1 to 10, wherein the first layer has a thickness of 0.3 to 20 µm. The polyester film for solar cell backsheets according to any one of claims 1 to 11, wherein a difference in intrinsic viscosity between the first layer and the second layer is 0.01 or more. The solar cell using the polyester film for solar cell backsheets of any one of Claims 1-12.

Images