JP2017157831A - Solar battery backside protection sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solar battery backside protection sheet which is superior in productivity which enables the suppression of powdering of a solar battery backside protection sheet after exposure to ultraviolet light over a long period of time.SOLUTION: A solar battery backside protection sheet comprises a layer (P1 layer) for a surface layer on at least one side, which includes a polyester resin as a main constituent, and it satisfies the requirement (1) below. (1) ΔH given by the formula (i), ΔH=H1-H0 is 5-30%, where H0 is a haze value measured by a haze meter on a length of tape peeled off in a tape peeling test executed on a surface of the P1 layer, and H1 is a haze value measured by a haze meter on a length of tape peeled in the tape peeling test conducted after performing a process for exposing the surface of the P1 layer to ultraviolet light.SELECTED DRAWING: Figure 1

Description

  The present technology relates to a solar cell back surface protective sheet that is excellent in suppressing powder blowing even when exposed to an outdoor environment for a long period of time.

  Solar cells, a representative renewable energy, have achieved significant market growth over the past few years due to the rapid spread of rooftop solar cells at the general household level. In addition, mega solar construction, which is a field-installed solar cell, is currently underway mainly by corporations and governments, and the continued introduction of solar cells and market expansion are expected. Silicon type solar cells, which are currently mainstream, use a transparent sealing material such as ethylene-vinyl acetate copolymer (hereinafter sometimes referred to as EVA) as a power generation element made of an inorganic semiconductor such as single crystal silicon or polycrystalline silicon. The light receiving surface side is sandwiched between resin sheets called a transparent glass substrate and a back surface side back sheet (a solar cell back surface protection sheet).

  Solar cells are installed in an outdoor environment where a large amount of sunlight, including ultraviolet rays, shines, and are exposed to stresses such as temperature and humidity changes and rain and wind accompanying natural climate changes for a long time. In order to protect the power generation element from these stresses, biaxially stretched polyethylene terephthalate (hereinafter sometimes referred to as “PET”) has been used as a solar cell back surface protection sheet that is inexpensive, has excellent weather resistance and electrical insulation, and has high strength. It was. So far, in addition to improving the solar cell power generation due to the improved design and light reflection characteristics of the solar cell, the surface of the solar cell back surface protection sheet (solar cell back side surface layer) from the viewpoint of suppressing degradation of the polyester resin due to UV exposure ), A white polyester film (Patent Documents 1-3) containing a large amount of a white pigment having an ultraviolet absorbing ability has been developed and is still used as a sheet for protecting the back surface of solar cells.

JP 2013-010363 A International Publication No. 2013/051661 JP 2012-019070 A

However, as a result of intensive studies by the present inventors, it has been found that a polyester film containing a large amount of these white pigments has the following problems.
When a polyester film containing a large amount of white pigment is placed in an outdoor environment for a long period of time, the polyester resin constituting the polyester film undergoes photodegradation (UV degradation) by exposure to ultraviolet rays. Polyester resin that has been photodegraded (UV deteriorated) cannot be retained in the form of a film because it is naturally vaporized from the surface layer by being decomposed to low molecular weight compounds, or the portion having low molecular weight is embrittled, such as wind and rain. It disappears by flowing down due to the external force (polyester film is eroded from the surface layer and the thickness decreases). Therefore, in a polyester film containing a large amount of white pigment, the white pigment embedded in the resin protrudes to the resin surface layer, and the appearance (color tone) changes, and the white pigment is white powder together with the deteriorated polyester resin. A problem of powder blowing phenomenon (white powder generation) occurs. The problem of the occurrence of white powder leads to a decrease in the UV resistance of the remaining solar cell back surface protection sheet, and in addition to reducing the life of the solar cell back surface protection sheet, also leads to environmental pollution near the solar cell location. .
In the case of Patent Document 1, the stretching temperature in the longitudinal direction (longitudinal direction, that is, the traveling direction of the sheet) at the time of film formation is high, and the crystallization of the polyester resin component proceeds. In the subsequent stretching process, the crystallization site becomes the starting point in the sheet. Many minute voids are formed, and the powder blowing suppression effect may be insufficient.

  In the case of Patent Document 2, the particle diameter of the added titanium oxide is large, and fine voids are easily formed during stretching, so that the effect of suppressing powder blowing may be insufficient. In addition, when the particle diameter is increased, the sum of the absorption cross-sectional areas of the particles with respect to ultraviolet rays may be reduced, and the change in color tone of the sheet after exposure to ultraviolet rays may be deteriorated.

  In the example of Patent Document 3, in addition to the large particle diameter of the added titanium oxide, the stretch ratio in the longitudinal direction (longitudinal direction, that is, the traveling direction of the sheet) at the time of film formation is high, and there is a minute amount around the added particles. Since many voids are formed, the powder blowing suppression effect may be insufficient.

  In view of these problems, an object of the present invention is to provide a solar cell back surface protective sheet that suppresses powder blowing even when exposed to an outdoor environment for a long period of time with high productivity.

In order to solve the above problems, the present invention has the following configuration. That is, 1. A sheet for protecting a back surface of a solar cell, which has a layer (P1 layer) having a polyester resin as a main constituent component on at least one surface layer and satisfies the following (1).
(1) The P1 layer surface was subjected to a tape peeling test under the following conditions, and the peeled tape was measured with a haze meter under the following conditions, the haze value was H0, and the P1 layer surface was subjected to ultraviolet irradiation treatment under the following conditions. When the haze value is H1 when the tape peel test was conducted later under the following conditions and the peeled tape was measured with a haze meter under the following conditions, ΔH represented by the formula (i) is 5% or more and 30% or less. There is.
Formula (i) (DELTA) H = H1-H0
<< Tape peeling test conditions >>
On the surface on the P1 layer side of the sheet for protecting the back surface of the solar cell, Sekisero Tape (registered trademark) No. 252 (manufactured by Sekisui Chemical Co., Ltd., tape width: 15 mm) is pasted and pressed using a 2 kg rubber roller, and then peeled 180 degrees at a speed of 0.12 m / min to 0.18 m / min.
<< Haze measurement conditions >>
Based on JIS-K7105 (1981), the Sekisui Cello Tape (registered trademark) peeled from the P1 layer was subjected to the thickness of the cello tape (registered trademark) using a fully automatic direct reading haze computer HGM-2DP (manufactured by Suga Test Instruments Co., Ltd.). Measure haze (%) in the vertical direction. The average of the three measurements is taken as the haze value.
<Ultraviolet irradiation treatment conditions>
Installed so that the test light hits the surface on the P1 layer side of the solar cell back surface protection sheet, using an i-super ultraviolet tester S-W161 (manufactured by Iwasaki Electric Co., Ltd.), temperature 60 ° C., relative humidity 50 R%, Irradiation is performed for 72 hours under conditions of illuminance of 150 mW / cm ² (light source: metal halide lamp, wavelength range: 295 to 450 nm, peak wavelength: 365 nm, conforming to JIS-C-1613).
2. The polyester resin and P2 layer which have adjacently the layer (P1 layer) which has the said polyester resin as a main component, and the base material layer (P2 layer) which has a polyester resin as a main component are adjacent. Both of the polyester resins constituting the white pigment contain a white pigment, and the white pigment content of the polyester resin constituting the P1 layer is 6% by mass or more and 13% by mass or less. The solar cell back surface protection sheet according to 1.
3. 1. The thickness of the P1 layer is 10% or more and 30% or less with respect to the total thickness of the P1 layer and the P2 layer. The solar cell back surface protection sheet according to 1.
4). 1. The white pigment contained in the P1 layer and the P2 layer is both titanium oxide, and the number average particle diameter thereof is 0.1 μm or more and less than 0.3 μm. The solar cell back surface protection sheet according to 1.
5. 4. The polyester resin composition constituting the P1 layer contains phosphoric acid and an alkali metal phosphate, and the phosphorus element content P (mol / t) is 1.8 mol / t or more to the entire polyester resin. 0 mol / t or less, containing at least one kind of metal element of Mn and Ca, and the content of divalent metal elements other than Mn and Ca is 5 ppm or less with respect to the whole polyester resin, When the content of the alkali metal element with respect to the entire polyester resin is M1 (mol / t), and the total of the Mn element content and the Ca element content with respect to the entire polyester resin is M2 (mol / t), the following formula ( The metal content M (mol / t) in the polyester resin and the phosphorus element content P (mol / t) obtained in ii) are expressed by the following formula ( 1 and satisfies the ii). ~ 2. The sheet | seat for solar cell back surface protection in any one of.
Formula (ii) M = M1 / 2 + M2
Formula (iii) 1.1 ≦ M / P ≦ 3.0
6). 1. The film thickness reduction amount (ΔL) when the xenon lamp irradiation test is performed on the surface of the P1 layer under the following conditions for 2000 hours is 5 μm or less. ~ 5. The sheet | seat for solar cell back surface protection in any one of.
<Xenon lamp irradiation test conditions>
A super xenon weather meter (Suga Test Instruments Co., Ltd.) with a solar cell back surface protection sheet installed so that the test light hits the P1 layer side surface, and a quartz glass filter as the filter and a daylight filter as the outer Xenon lamp under the conditions of irradiation intensity of 180 W / m ² (300-400 nm), temperature (black panel temperature) of 63 ° C., and relative humidity of 50% in accordance with JIS-K-7350-2 (2008). The irradiation test is performed for 2000 hours. In this test, a cycle (one cycle 120 minutes) in which the spraying process using the spray device built in the apparatus is performed every 102 minutes for 18 minutes while continuing the xenon lamp irradiation is repeated 1000 times.
<< Measurement conditions for film thickness reduction >>
A sheet for protecting the back surface of the solar cell is cut into a rectangle 6 cm long and 7 cm wide. Measure the thickness of a total of 5 points with a thickness meter at the center of the rectangular sample and 4 points 1.5 cm in the vertical direction and 2 cm in the horizontal direction, and average the thickness of these 5 points to the xenon lamp irradiation test The previous sheet thickness (L0) is used.
The rectangular sample is subjected to the above xenon lamp irradiation test for 2000 hours, and then the sheet thickness is measured by the same method as described above, and the obtained value is defined as the sheet thickness (L1) after the xenon lamp irradiation test. Using L0 and L1, the film thickness reduction amount (ΔL) is obtained from the following equation (9).
Film thickness reduction amount (ΔL) = L1-L0 (9)
7.1. ~ 6. A solar cell module comprising the solar cell back surface protective sheet according to any one of the above.

  ADVANTAGE OF THE INVENTION According to this invention, even if it exposes for a long time in outdoor environment, the solar cell back surface protection sheet which suppressed powder blowing, and a solar cell using the same can be provided.

It is sectional drawing which shows typically an example of a structure of the solar cell using the solar cell back surface protection sheet of this invention.

The solar cell back surface protection sheet of the present invention has a layer (P1 layer) containing a polyester resin as a main constituent component on at least one surface layer, and satisfies the following condition (1).
(1) The P1 layer surface was subjected to a tape peeling test under the following conditions, and the peeled tape was measured with a haze meter under the following conditions, the haze value was H0, and the P1 layer surface was subjected to ultraviolet irradiation treatment under the following conditions. When the haze value is H1 when the tape peel test was conducted later under the following conditions and the peeled tape was measured with a haze meter under the following conditions, ΔH represented by the formula (i) is 5% or more and 30% or less. There is.
Formula (i) (DELTA) H = H1-H0
<< Tape peeling test conditions >>
On the surface on the P1 layer side of the sheet for protecting the back surface of the solar cell, Sekisero Tape (registered trademark) No. 252 (manufactured by Sekisui Chemical Co., Ltd., tape width: 15 mm) is pasted and pressed using a 2 kg rubber roller, and then peeled 180 degrees at a speed of 0.12 m / min to 0.18 m / min.
<< Haze measurement conditions >>
Based on JIS-K7105 (1981), the Sekisui Cello Tape (registered trademark) peeled from the P1 layer was subjected to the thickness of the cello tape (registered trademark) using a fully automatic direct reading haze computer HGM-2DP (manufactured by Suga Test Instruments Co., Ltd.). Measure haze (%) in the vertical direction. The average of the three measurements is taken as the haze value.
<Ultraviolet irradiation treatment conditions>
Installed so that the test light hits the surface on the P1 layer side of the solar cell back surface protection sheet, using an i-super ultraviolet tester S-W161 (manufactured by Iwasaki Electric Co., Ltd.), temperature 60 ° C., relative humidity 50 R%, Irradiation is performed for 72 hours under conditions of illuminance of 150 mW / cm ² (light source: metal halide lamp, wavelength range: 295 to 450 nm, peak wavelength: 365 nm, conforming to JIS-C-1613).

(P1 layer (hereinafter sometimes referred to as a weather-resistant layer))
First, the P1 layer of the solar cell back surface protective sheet of the present invention contains a polyester resin as a main component. Here, the main constituent component of the polyester resin means that the polyester resin is contained in an amount exceeding 50% by mass with respect to the resin constituting the P1 layer. Specific examples of the polyester resin constituting the P1 layer include polyethylene terephthalate, polyethylene-2, 6-naphthalate, polypropylene terephthalate, polybutylene terephthalate, and polylactic acid. The polyester resin used in the present invention includes 1) polycondensation of dicarboxylic acid or an ester-forming derivative thereof (hereinafter collectively referred to as “dicarboxylic acid component”) and a diol component, and 2) carboxylic acid or carboxylic acid in one molecule. It can be obtained by a polycondensation of an acid derivative and a compound having a hydroxyl group, and 1) 2). The polymerization of the polyester resin can be performed by a conventional method.

  In 1), examples of the dicarboxylic acid component include, but are not limited to, dicarboxylic acids such as aliphatic dicarboxylic acids, alicyclic dicarboxylic acids, and aromatic dicarboxylic acids, and ester derivatives thereof. Examples of the aliphatic dicarboxylic acids include malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecanedioic acid, dimer acid, eicosandioic acid, pimelic acid, azelaic acid, methylmalonic acid, ethyl And malonic acid. Examples of the alicyclic dicarboxylic acids include adamantane dicarboxylic acid, norbornene dicarboxylic acid, isosorbide, cyclohexane dicarboxylic acid, decalin dicarboxylic acid, and the like. Examples of the aromatic dicarboxylic acid include terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, and 1,8-naphthalenedicarboxylic acid. Acid, 4,4′-diphenyl dicarboxylic acid, 4,4′-diphenyl ether dicarboxylic acid, 5-sodium sulfoisophthalic acid, phenyl endandicarboxylic acid, anthracene dicarboxylic acid, phenanthrene dicarboxylic acid, 9,9′-bis (4-carboxyl) Phenyl) fluoric acid and the like. These may be used alone or in combination.

  In addition, dicarboxyl obtained by condensing at least one carboxy terminus of the above dicarboxylic acid component with oxyacids such as l-lactide, d-lactide, and hydroxybenzoic acid, and derivatives thereof or a combination of a plurality of such oxyacids. Compounds can also be used.

  Next, examples of the diol component include diols such as aliphatic diols, alicyclic diols, and aromatic diols, and those in which a plurality of such diols are linked, but are not limited thereto. It is not a thing. Examples of the aliphatic diols include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-butanediol, 1,3-butanediol, and the like. . Examples of the alicyclic diols include cyclohexanedimethanol, spiroglycol, and isosorbide. Examples of aromatic diols include bisphenol A, 1,3-benzenedimethanol, 1,4-benzenedimethanol, 9,9'-bis (4-hydroxyphenyl) fluorene, and the like. Moreover, these may be used independently or may be used in multiple types as needed. In addition, a dihydroxy compound formed by condensing a diol with at least one hydroxy terminal of the diol component described above can also be used.

  In 2), examples of compounds having a carboxylic acid or a carboxylic acid derivative and a hydroxyl group in one molecule include oxyacids such as l-lactide, d-lactide and hydroxybenzoic acid, and derivatives thereof, oligomers of oxyacids, dicarboxylic acids Examples thereof include those obtained by condensing an oxyacid with one carboxyl group of the acid.

  The dicarboxylic acid component and the diol component constituting the polyester resin may be selected and copolymerized one by one from the above, or a plurality of each may be selected and copolymerized.

The polyester resin constituting the P1 layer may be a single type or a blend of two or more types of polyester resins.
It is preferable that the polyester resin which comprises P1 layer of the solar cell back surface protection sheet of this invention contains a phosphoric acid alkali metal phosphate and phosphoric acid as a phosphorus compound. Examples of the alkali metal phosphate include sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, tripotassium phosphate, lithium dihydrogen phosphate, Examples include dilithium hydrogen phosphate and trilithium phosphate. Preferred are alkali metal dihydrogen phosphate and dialkali metal hydrogen phosphate. Moreover, the alkali metal phosphate whose alkali metal element is Na and K is preferable from the viewpoint of long-term wet heat resistance. Particularly preferred are sodium dihydrogen phosphate and potassium dihydrogen phosphate.

  The polyester resin constituting the P1 layer of the solar cell back surface protection sheet of the present invention has a phosphorus element content P of 1.8 mol / t or more and 5.0 mol / t or less with respect to the entire polyester resin. preferable. Further, the polyester resin contains at least one kind of metal element of Mn and Ca, and the content of other divalent metal elements is 5 ppm or less with respect to the whole polyester resin at most. preferable. Here, the metal element includes not only atoms but also those present in the polyester resin in an ionic state. In general, the metal element exists in an ionic state in the polyester resin.

Moreover, the polyester resin which comprises P1 layer of the solar cell back surface protection sheet | seat of this invention makes content of the alkali metal element with respect to the whole polyester resin M1 (mol / t), Mn element content with respect to the whole polyester resin, and Ca When the total element content is M2 (mol / t), the metal content M (mol / t) obtained by the following formula (1) and the phosphorus element content P (mol / t) are as follows. It is preferable to satisfy the formula (ii).
M = (M1) / 2 + M2 Formula (ii)
1.1 ≦ M / P ≦ 3.0 Formula (iii)
The above-mentioned divalent metal elements are alkaline earth metal elements up to the third period of the chemical periodic table, elements from the first group to the twelfth group after the fifth period, and transition metals in the fourth period excluding Ti. Refers to an element. The valence of the metal element in the present invention is the total number of electrons existing in the outermost shell or the s orbital closest to the outermost shell among the electron orbits of the metal atoms.

  The Mn element and Ca element contained in the polyester resin are preferably metal compounds containing these metal elements. These metal compounds have a function as a transesterification reaction catalyst.

  The polyester resin constituting the P1 layer of the solar cell back surface protective sheet of the present invention is a group consisting of a metal compound containing at least one metal element selected from the group consisting of Na, Li and K, and Sb, Ti and Ge. It is preferable that the total of the content of these metal elements is 30 ppm or more and 2000 ppm or less with respect to the whole polyester resin. By making the total content of metal elements within this range, the amount of COOH end groups can be suppressed, and the heat resistance is improved. Na, Li, and K are alkali metal elements. Sb, Ti and Ge are metal elements having a polymerization catalyst ability and function as a polymerization catalyst.

  The polyester resin which comprises P1 layer of the solar cell back surface protection sheet | seat of this invention contains both the alkali metal phosphate and phosphoric acid as a phosphorus compound as above-mentioned. According to such a configuration, the activity of the COOH end group of the polyester is reduced due to the buffering action, and as a result of suppressing the progress of hydrolysis in a moist heat atmosphere, the moist heat resistance can be greatly improved. This effect not only increases the heat and moisture resistance of the solar cell back surface protection sheet formed, but also exhibits an effect during the production of a master pellet containing a white pigment described later.

  In the polyester resin constituting the P1 layer of the solar cell back surface protective sheet of the present invention, the phosphorus element content P is preferably 1.8 mol / t or more and 5.0 mol / t or less with respect to the entire polyester resin. . If the content P of the phosphorus element is less than 1.8 mol / t, the content of the alkali metal phosphate and phosphoric acid is not sufficient, and thus the increase in the amount of COOH end groups in a humid heat atmosphere cannot be suppressed. Further, the hydrolysis of the polyester resin tends to proceed, and there is a possibility that the heat and humidity resistance is lowered. If the phosphorus element content P exceeds 5.0 mol / t, the alkali metal phosphate and / or phosphoric acid content becomes excessive. When the alkali metal phosphate is excessive, there is a concern that the alkali metal phosphate becomes a foreign substance. When phosphoric acid is excessive, the polymerization catalyst is deactivated by the phosphoric acid, the polymerization reaction is delayed, and the COOH terminal Since the base amount is increased, the heat and moisture resistance of the polyester resin may be lowered. Further, the content of the alkali metal phosphate in the polyester resin is preferably 1.3 mol / t or more and 3.0 mol / t or less with respect to the entire polyester resin from the viewpoint of heat and moisture resistance. Moreover, it is preferable from the point of long-term wet heat resistance that content of phosphoric acid is 0.4 times or more and 1.5 times or less with respect to alkali metal phosphate.

  The alkali metal element, Mn element, and Ca element contained in the polyester resin constituting the P1 layer of the solar cell back surface protective sheet of the present invention are chemically bonded to a phosphorus element-containing compound or a polyester COOH terminal group, and a phosphorus compound This suppresses the deactivation of the polymerization catalyst by, and suppresses the autocatalysis of the COOH end group, thereby suppressing the hydrolysis. The alkali metal element is effective in suppressing deactivation of the polymerization catalyst, and the Mn element and Ca element are effective in suppressing deactivation of the polymerization catalyst and hydrolysis due to suppression of the autocatalytic action of the COOH end group.

  In general, metal ions contained in a polyester resin are chemically bonded to carbonyl groups including COOH end groups. In particular, when a metal ion is chemically bonded to the carbonyl group of the COOH end group, the presence of water molecules causes the autocatalytic action of the COOH end group, thereby causing hydrolysis and deterioration of the polyester. In order to suppress this hydrolysis, it is effective to stabilize metal ions chemically bonded to the COOH end groups and water molecules. That is, it is effective to hydrate metal ions and water molecules. As an index of this effect, the product of the hydration enthalpy of the metal ion and the radius of the metal ion can be used. Mn, Ca, and Al ions can be cited as metal elements having a large product value. These metal ions can stabilize water molecules more effectively, and as a result, can improve the heat and moisture resistance of the polyester resin. In particular, a compound of Mn element and Ca element is more preferable as a metal element to be contained because of its high performance as a transesterification reaction catalyst.

Moreover, since a phosphorus compound exists as an anion in a polyester resin, it chemically bonds with a metal element that exists in an ionic state in the polyester resin. When the anion derived from the phosphorus compound is chemically bonded to the metal element ion derived from the polymerization catalyst, the polymerization catalyst is deactivated. In the polyester resin, the presence of metal element ions other than the metal element derived from the polymerization catalyst can suppress the chemical bond between the metal element ion derived from the polymerization catalyst and the anion derived from the phosphorus compound, Deactivation of the polymerization catalyst can be suppressed. Here, M / P represented by the above-mentioned formula (2) serves as an index for suppressing polymerization catalyst deactivation by a phosphorus compound or suppressing autocatalysis of a COOH end group of a polyester resin. M in this formula represents the content of ions of metal elements that are chemically bonded to anions derived from phosphorus compounds in the polyester resin.
However, since the anion derived from the phosphorus compound in the polyester resin is divalent, it interacts 1: 1 with the cation of the divalent metal element. Therefore, it is necessary to multiply the content M1 of the metal element that becomes a monovalent cation in the polyester resin by a coefficient of 0.5.

  In the polyester resin which comprises P1 layer of the solar cell back surface protection sheet of this invention, it is preferable that M / P is 1.1 or more and 3.0 or less. If it is less than 1.1, the amount of the metal element relative to the amount of the phosphorus compound is too small, and the suppression of the deactivation of the polymerization catalyst by the phosphorus compound or the suppression of the autocatalysis of the COOH end group of the polyester resin is not sufficient. The amount of COOH end groups increases, the progress of the hydrolysis reaction under a moist heat atmosphere cannot be suppressed, and the moist heat resistance may be lowered. Moreover, when M / P exceeds 3.0, the compound containing a metal element becomes excessive, and there exists a possibility that it may become a foreign material. By setting M / P within the above range, a polyester resin having few foreign matters and excellent moisture and heat resistance can be obtained. M / P is more preferably 1.15 or more and 1.4 or less.

  As above-mentioned, in the polyester resin which comprises P1 layer of the solar cell back surface protection sheet of this invention, content of bivalent metal elements other than Mn and Ca is 5 ppm or less with respect to the whole polyester resin, respectively. When the content of any of the divalent metal elements other than Mn element and Ca element exceeds 5 ppm with respect to the whole polyester resin, the deactivation suppression effect of the polymerization catalyst by Mn element and Ca element There is a possibility that the self-catalyst suppressing action of the COOH end group is hindered and the heat and humidity resistance is lowered. More preferably, the total content of divalent metal elements other than Mn element and Ca element is 5 ppm or less.

  In the polyester resin constituting the P1 layer of the solar cell back surface protection sheet of the present invention, a heat resistance stabilizer, an oxidation resistance stabilizer, an ultraviolet absorber, an ultraviolet light stabilizer, an organic system, as long as the effects of the present invention are not impaired. / Inorganic lubricants, organic / inorganic fine particles, fillers, nucleating agents, dyes, dispersants, coupling agents, and other additives may be blended.

  The resin constituting the P1 layer of the solar cell back surface protective sheet of the present invention is mainly composed of a polyester resin as described above, but the intrinsic viscosity (IV) of the polyester resin is 0.60 dl / g or more and 0.80 dl. / G or less is preferable. Moreover, it is preferable that the amount of terminal carboxyl groups is 25 equivalents / ton or less. The polyester resin is preferably composed mainly of polyethylene terephthalate (PET). Here, the main component means that it is contained in excess of 50% by mass with respect to the polyester resin. When the resin constituting the P1 layer contains PET as a main constituent, the intrinsic viscosity (IV) of the PET is preferably 0.65 dl / g or more, more preferably 0.69 dl / g or more. When the intrinsic viscosity (IV) is less than 0.65 dl / g, the moisture and heat resistance of the sheet may deteriorate. Moreover, when intrinsic viscosity (IV) exceeds 0.80 dl / g, when the P1 layer is manufactured, the extrudability of the resin may be poor, and sheet molding may be difficult. Furthermore, even if the intrinsic viscosity (IV) satisfies the above range, if the terminal carboxyl group amount exceeds 25 equivalents / ton, the adhesion to the P2 layer is improved, but the moisture and heat resistance of the sheet may be deteriorated. . Therefore, when the resin constituting the P1 layer contains PET as the main constituent, the sheet for protecting the back surface of the solar cell is excellent in moldability and long-term durability by setting the intrinsic viscosity and the amount of terminal carboxyl groups within the above ranges. It can be.

  In the solar cell back surface protective sheet of the present invention, the number average molecular weight of the polyester resin constituting the P1 layer is preferably 8000 to 40000, more preferably 9000 to 30000, and still more preferably 10,000 to 25000. Here, the number average molecular weight of the polyester resin constituting the P1 layer refers to the gel permeation chromatography method by separating the P2 layer from the solar cell back surface protective sheet of the present invention and dissolving it in hexafluoroisopronol (HFIP). It is a value obtained by using polyethylene terephthalate and dimethyl terephthalate having a known molecular weight as standard samples from values measured by a GPC method and detected by a differential refractometer. When the number average molecular weight of the polyester resin constituting the P1 layer is less than 8000, it is not preferable because the long-term durability of the sheet such as moisture and heat resistance may be deteriorated. On the other hand, if it exceeds 40,000, even if the polymerization is difficult or the polymerization can be performed, it may be difficult to extrude the resin with an extruder and film formation may be difficult. In the solar cell back surface protective sheet of the present invention, the P1 layer is preferably uniaxially or biaxially oriented. When the P1 layer is uniaxially or biaxially oriented, the long-term durability of the sheet such as moist heat resistance and heat resistance can be improved by orientation crystallization.

(White pigment)
The P1 layer of the solar cell back surface protective sheet of the present invention preferably contains a white pigment for the purpose of imparting properties such as light reflectivity, light hiding properties, design properties, and visibility. In order to achieve both the color tone change after exposure to ultraviolet rays and the suppression of powder blowing in addition to the above-mentioned characteristics, a white pigment should be contained in the range of 6% by mass to 13% by mass with respect to the resin constituting the P1 layer. Is preferred. If the content of the white pigment is less than 6% by mass, the change in color tone after irradiation with ultraviolet rays may be deteriorated, and the amount of film thickness reduction associated with deterioration and decomposition vaporization of the surface layer polyester resin described later may increase. If it is more than 13% by mass, adhesion to the P2 layer described later may be deteriorated and film formation may be difficult. As a more preferable range, it is 8 mass% or more and 12 mass% or less, More preferably, it is 10 mass% or more and 12 mass% or less. Preferred examples of the white pigment include silica, calcium phosphate, titanium oxide, barium sulfate, silicon oxide, aluminum oxide, magnesium oxide, calcium carbonate, kaolin, talc, clay, mica, alumina and zirconia, and aluminosilicate particles. . It is more preferable to use rutile-type titanium oxide from the viewpoint of achieving both ultraviolet absorption ability and light reflectivity.

  The average particle diameter of the white pigment contained in the P1 layer of the solar cell back surface protective sheet of the present invention is 0.1 μm or more and less than 0.3 μm from the viewpoint of achieving both the ultraviolet durability of the P1 layer and the suppression of powder blowing. Is preferred. Here, the average particle diameter of the white pigment refers to a number-based average particle diameter obtained by a measurement method using a field emission scanning electron microscope (SEM) described later. When the average particle size of the white pigment is less than 0.1 μm, the cohesive force of the white pigment increases, so that the dispersibility of the white pigment in the master pellet and P1 layer described later deteriorates and the catalytic activity of the white pigment increases. In some cases, the polyester resin is decomposed by the photocatalytic reaction, so that it is difficult to suppress powder blowing, and the surface layer polyester resin described later may increase the amount of film thickness reduction due to deterioration and decomposition vaporization. In addition, when the average particle size of the white pigment is 0.3 μm or more, the amount of minute voids formed around the white pigment increases due to stretching during film formation, which may make it difficult to suppress powder blowing.

(Master pellet manufacturing method)
As a method of including the white pigment in the polyester resin constituting the P1 layer of the solar cell back surface protection sheet of the present invention, the polyester resin and the white pigment are bent using a bent type twin-screw kneading extruder or a tandem type extruder. A method of producing a pellet (master pellet) in which a white pigment is melt-kneaded and dispersed in a polyester resin is preferably used. Here, when the polyester resin is subjected to a heat load when the polyester resin contains particles, the polyester resin deteriorates due to thermal degradation and hydrolysis due to slight moisture contained in the polyester resin and the white pigment to be kneaded. To do. Therefore, a high-concentration master pellet having a white pigment content higher than that of the white pigment contained in the polyester resin constituting the P1 layer is prepared, mixed with the polyester resin and diluted to obtain a desired particle content. It is preferable to produce a layer from the viewpoint of heat and moisture resistance and reduction of heat-deteriorated foreign matter during film formation.
Here, when producing a high concentration white pigment master pellet, the white pigment dispersibility depends on the shear stress by the screw during melt kneading. In order to increase the dispersibility by applying a force higher than the cohesive force of the pigment, kneading with a high shear stress is one means of accomplishment, but as a trade-off, the load due to the shear heat on the polyester resin increases. It is also possible to create master pellets by two-stage melt-kneading, once the master pellets are prepared at a low concentration to ensure the dispersibility of the white pigment, and then the white pigment is added again and raised to the desired concentration. Although this method is used as an improvement method, this method also has a tradeoff with dispersibility because the heat load on the polyester resin increases.
In the solar cell back surface protection sheet of the present invention, the method for preparing the high concentration master pellet added to the P1 layer is prepared through the above-described high shear kneading and the two-stage kneading step from the viewpoint of enhancing the dispersibility of the white pigment. It is preferable to use the master pellet. This is because if the dispersibility is low at the time of the master pellet, the average particle size of the white pigment in the P1 layer increases due to poor dispersion, and the amount of microscopic voids that accompanies stretching increases. The generation of the air gap also affects the increase in the film thickness reduction amount ΔL described later.
In particular, when a polyester resin satisfying the above-mentioned formulas (1) and (2) is used as a base resin, a high concentration white pigment master pellet prepared by applying a high shear stress and undergoing a two-stage kneading process is obtained. It was found that the generation of foreign matter during film formation of the solar cell back surface protection sheet was suppressed, and the generation of voids inside the P1 layer was suppressed.
The white pigment concentration of the master pellet is preferably 50% by mass or less. When the concentration is higher than 50% by mass, the above-mentioned polyester resin and master pellet manufacturing method can be used to suppress powder blowing by improving the dispersibility of the white pigment in the P1 layer and to suppress the occurrence of resin-deteriorated foreign matter during film formation. It was difficult to achieve both.

  Furthermore, in order to improve the ultraviolet resistance, light hiding property, and design, 0.1 particles (hereinafter referred to as carbon particles) made of a carbon-based material such as fullerene, carbon fiber, or carbon nanotube are used as the resin constituting the P1 layer. It is preferable to contain in the range of mass% or more and 5 mass% or less. This makes it possible to exhibit the effect of reducing coloring due to deterioration of the sheet for protecting the back surface of the solar cell over a long period of time by making use of the ultraviolet absorbing ability and light hiding property of the carbon particles.

(P2 layer (hereinafter sometimes referred to as base material layer))
The solar cell back surface protective sheet of the present invention may be a single-layer film composed only of the P1 layer described above, or may be a laminated film having layers other than the P1 layer. It is preferable to have a base material layer (P2 layer) having a polyester resin as a main constituent component adjacent to one side of the P1 layer (weather-resistant layer). Adjacent to one side of the P1 layer (weather-resistant layer) is a base material layer (P2 layer) mainly composed of a polyester resin, thereby improving the moldability and electrical insulation of the solar cell back surface protection sheet. Can be improved.

The P2 layer of the solar cell back surface protective sheet of the present invention contains a polyester resin as a main component. Here, the main constituent component of the polyester resin means that the polyester resin is contained in an amount exceeding 50% by mass with respect to the resin constituting the P2 layer. The polyester resin constituting the P2 layer is composed of the dicarboxylic acid component and the diol component described in the above section (P1 layer), specifically, polyethylene terephthalate, polyethylene-2, 6-naphthalate, Examples thereof include polypropylene terephthalate, polybutylene terephthalate, and polylactic acid.
The polyester resin constituting the P2 layer may be a single type or a blend of two or more types of polyester resins.
The resin constituting the P2 layer of the solar cell back surface protection sheet of the present invention is mainly composed of a polyester resin as in the above-described P1, but the intrinsic viscosity (IV) of the polyester resin is the moldability of the P1 layer. For the purpose of assisting, it is preferable to lower the intrinsic viscosity as compared with the P1 layer. Specifically, it is preferably 0.55 dl / g or more and 0.75 dl / g or less. Moreover, it is preferable that the amount of terminal carboxyl groups is 40 equivalent / tons or less. The polyester resin is preferably composed mainly of polyethylene terephthalate (PET). Here, the main component means that it is contained in excess of 50% by mass with respect to the polyester resin. When the resin constituting the P2 layer contains PET as the main constituent, the intrinsic viscosity (IV) of the PET is preferably 0.58 dl / g or more, more preferably 0.60 dl / g or more. When the intrinsic viscosity (IV) is less than 0.55 dl / g, the moisture and heat resistance of the sheet may be deteriorated even when the P1 layer is laminated. When the intrinsic viscosity (IV) exceeds 0.80 dl / g, the extrudability of the resin may be poor when the P2 layer is produced, and sheet molding may be difficult. Furthermore, even if the intrinsic viscosity (IV) satisfies the above range, if the amount of terminal carboxyl groups exceeds 35 equivalents / ton, the sealing material layer or the sealing material easy-adhesion layer on the side not in contact with the P1 layer of the P2 layer In the case where the sheet is provided, the adhesion to each layer is improved, but the moisture and heat resistance of the sheet may be deteriorated even when the P1 layer is laminated. Therefore, when the resin constituting the P2 layer is mainly composed of PET, by setting the intrinsic viscosity and the amount of terminal carboxyl groups within the above ranges, the sheet has excellent sheet moldability and long-term durability. It can be a sheet.
Although there is no restriction | limiting in particular regarding the phosphorus element amount contained in the P2 layer of the solar cell back surface protection sheet of this invention, and a metal element amount, When improving the heat-and-moisture resistance of the solar cell back surface protection sheet of this invention, it is a polyester resin. It is preferable to use a polyester containing the element amount described in the item of polymerization catalyst in the P1 layer.
The P2 layer of the solar cell back surface protection sheet of the present invention is given a white pigment for the purpose of imparting properties such as ultraviolet resistance, light reflectivity, light hiding properties, design properties, visibility, or assisting the properties of the P1 layer. It is preferable to contain. It is preferable to contain a white pigment in the range of 0.1% by mass or more and less than 6% by mass with respect to the resin constituting the P1 layer. If the content of the white pigment is less than 0.1% by mass, the light reflectivity may be insufficient and the solar cell back surface protection sheets may be blocked during film formation. If the content is more than 6% by mass, the moldability during film formation may be reduced. In some cases, it is difficult to improve the electrical insulation, and the improvement in electrical insulation may be hindered. A more preferable range is 0.5% by mass or more and 5% by mass or less, and further preferably 1% by mass or more and 2% by mass or less.
As the white pigment, those described in the section of the P1 layer can be suitably used, but it is more preferable to use rutile type titanium oxide from the viewpoint of imparting light reflectivity. As a method of incorporating the above white pigment into the polyester resin constituting the P2 layer, a polyester resin and particles are melt-kneaded using a vent type twin-screw kneading extruder or a tandem type extruder to produce a high concentration master pellet. It is preferable from the viewpoint of heat and humidity resistance to use a method of preparing a P2 layer having a desired particle content by mixing and diluting it with a polyester resin. Here, since the white pigment content of the P2 layer is low, the resin used for the master pellet is not particularly limited.

(Thickness ratio of P1 layer and P2 layer)
When the solar cell back surface protective sheet of the present invention includes a weather resistant layer (P1 layer) and a base material layer (P2 layer), the P1 layer thickness (d1) and the P2 layer thickness represented by the following formula (iii) ( The P1 layer thickness ratio (D (%)) to the sum of d2) is preferably 10% or more and 30% or less.
D (%) = d1 / (d1 + d2) Expression (iii)
When D (%) in the solar cell back surface protective sheet of the present invention is less than 10%, even if the change in the color tone of the P1 layer itself after UV irradiation is satisfactory, the color tone of the adjacent P2 layer after UV irradiation The change becomes large, and as a result, the color change of the P1 layer may become large as a result. Further, when the thickness ratio of the P1 layer exceeds 30%, the tear due to the P1 layer containing a large amount of particles may occur and productivity may decrease.
The P2 layer of the solar cell back surface protective sheet of the present invention may have a laminated structure for the purpose of imparting adhesiveness to other solar cell members such as a sealing material. For example, a method in which a layer having excellent adhesion (referred to as a P22 layer) is preferably used in advance on the side in contact with the P1 layer of the P2 layer (referred to as a P21 layer) that is a base material layer. In that case, the structure of the sheet is laminated in the order of P1 layer / P21 layer / P22 layer, and the thickness of the P2 layer is represented by P21 layer + P22 layer. At this time, the P21 layer is not particularly limited as long as the P21 layer has good adhesiveness to the resin constituting the P1 layer and the P22 layer, and the ratio of the polyester resin in the entire P2 layer (P21 layer + P22 layer) is 50% by mass or more.

(Solar cell backside protection sheet)
When the solar cell back surface protective sheet of the present invention has a P1 layer and a P2 layer (P1 layer / P2 layer), for example, a gas barrier property and an easy adhesion property on the surface of the P1 layer that is not adjacent to the P2 layer. A layer having other functions can be provided. As a method of providing these layers, a method of separately preparing materials to be laminated with the P1 layer and thermocompression bonding with a heated group of rolls (thermal laminating method), a method of bonding together with an adhesive (adhesion method) ) In addition, a method of dissolving the material for forming the material to be laminated in a solvent and applying the solution onto the P1 layer prepared in advance (coating method), electromagnetic wave irradiation after applying a curable material onto the P1 layer A method of curing by heat treatment or the like, a method of depositing / sputtering a material to be laminated on the P1 layer, a method of combining these, or the like can be used.

The solar cell back surface protection sheet of the present invention needs to have a P1 layer satisfying the following (1) on at least one surface layer.
(1) The P1 layer surface was subjected to a tape peeling test under the following conditions, and the peeled tape was measured with a haze meter under the following conditions, the haze value was H0, and the P1 layer surface was subjected to ultraviolet irradiation treatment under the following conditions. When the haze value is H1 when the tape peel test was conducted later under the following conditions and the peeled tape was measured with a haze meter under the following conditions, ΔH represented by the formula (i) is 5% or more and 30% or less. There is.
Formula (i) (DELTA) H = H1-H0
<< Tape peeling test conditions >>
On the surface on the P1 layer side of the sheet for protecting the back surface of the solar cell, Sekisero Tape (registered trademark) No. 252 (manufactured by Sekisui Chemical Co., Ltd., tape width: 15 mm) is pasted and pressed using a 2 kg rubber roller, and then peeled 180 degrees at a speed of 0.12 m / min to 0.18 m / min.
<< Haze measurement conditions >>
Based on JIS-K7105 (1981), Sekisui Cello Tape (registered trademark) peeled off from the P1 layer was measured using a fully automatic direct reading haze computer HGM-2DP (manufactured by Suga Test Instruments Co., Ltd.). Measure haze (%) in the vertical direction. The average of the three measurements is taken as the haze value.
<Ultraviolet irradiation treatment conditions>
Installed so that the test light hits the surface on the P1 layer side of the solar cell back surface protection sheet, using an i-super ultraviolet tester S-W161 (manufactured by Iwasaki Electric Co., Ltd.), temperature 60 ° C., relative humidity 50 R%, Irradiation is performed for 72 hours under conditions of illuminance of 150 mW / cm ² (light source: metal halide lamp, wavelength range: 295 to 450 nm, peak wavelength: 365 nm, conforming to JIS-C-1613).
The ultraviolet irradiation treatment in (1) is an accelerated test in a situation where a long period of exposure (equivalent to about 10 years) is exposed to an outdoor environment where a large amount of sunlight including ultraviolet rays falls.
The tape peeling test in (1) is a test that peels off after sticking an adhesive tape on the surface of a polyester film. The peeled adhesive tape has a polyester resin that has been whitened by photolysis (UV degradation) on the surface of the polyester film, and is white powdered with a slight external force as a result of photolysis (UV degradation) although it has not been whitened. Polyester resin adheres. Therefore, when a polyester film in which a large amount of white powder is generated by ultraviolet irradiation treatment is subjected to a tape peeling test, a large amount of white powder adheres to the peeled adhesive tape, and the haze of the adhesive tape to which a large amount of white powder adheres increases. Accordingly, the higher ΔH in the formula (i), the more white powder is generated on the surface of the polyester film by the ultraviolet irradiation treatment, and the lower ΔH is, the less white powder is generated on the surface of the polyester film by the ultraviolet irradiation treatment. .
In the solar cell back surface protection sheet of the present invention, the solar cell back surface protection sheet of the present invention was mounted when the amount of change in haze (ΔH) when the ultraviolet ray treatment test was performed using the P1 layer as the incident surface exceeded 30%. When a solar cell is placed outdoors for a long period of time, white powder is generated by exposure to ultraviolet light, leading to a decrease in the UV resistance of the weather-resistant layer in the solar cell back surface protection sheet, and the life of the solar cell back surface protection sheet is reduced. In addition to lowering, it also leads to environmental pollution near the solar cell location. On the other hand, when ΔH is less than 5%, white powder generation on the surface of the polyester film is suppressed, but the surface of the polyester film, not the surface of the polyester film, affects the inside of the polyester film, resulting in long-term outdoor use. Then, a crack, peeling, etc. generate | occur | produce and the durable use period of the solar cell back surface protection sheet falls. ΔH is more preferably 8% or more and 26% or less, and still more preferably 8% or more and 21% or less.
In the solar cell back surface protective sheet of the present invention, the method for setting ΔH to the above range is not particularly limited. For example, ΔH is adjusted by the content of the white pigment contained in the P1 layer, the type of white pigment, the particle diameter of the white pigment, the M / P contained in the polyester resin constituting the P1 layer, the film forming conditions of the polyester film, etc. it can.
As the content of the white pigment contained in the P1 layer increases, ΔH tends to increase because the amount of white powder increases when the surface layer of the polyester film deteriorates as the content increases. On the other hand, since the white pigment has the property of reflecting or absorbing the ultraviolet ray irradiated to the polyester film, if the content of the white pigment contained in the P1 layer is small, the inside of the polyester film depends on the ultraviolet ray. As a result, if it is used outdoors for a long period of time, cracks, peeling, etc. may occur, and the durable use period of the solar cell back surface protection sheet may be reduced. Further, as a type of white pigment, ΔH tends to be small when a white pigment having ultraviolet absorbing ability and ultraviolet reflecting ability (light reflectivity) is used.
Examples of white pigments having ultraviolet absorbing ability and ultraviolet reflecting ability (light reflectivity) include titanium oxide. Anatase-type titanium oxide has a large photocatalytic activity when absorbing ultraviolet rays, and tends to increase ΔH because the peripheral polyester resin is oxidized by a photocatalytic reaction to promote deterioration. On the other hand, rutile-type titanium oxide has a smaller photocatalytic activity than anatase type and does not promote oxidative degradation due to the photocatalytic reaction of polyester resin, and therefore tends to reduce ΔH. In addition, if the average particle size of the white pigment contained in the P1 layer is too small, the white pigment dispersibility deteriorates due to an increase in the cohesive force of the white pigment, and coarse particles are likely to be formed. Since the catalytic activity is increased and the polyester resin is promoted to decompose by the photocatalytic reaction, white powder is generated more and ΔH tends to be higher. Moreover, when the average particle diameter of the white pigment contained in the P1 layer is too large, when the polyester film containing the white pigment is stretched, fine voids are formed around the white pigment, and the amount of white powder generated is increased. Therefore, ΔH tends to increase. When the average particle diameter of the white pigment contained in the P1 layer is in the range of 0.1 μm to 0.3 μm, ΔH tends to be small. Moreover, since decomposition | disassembly of a polyester resin can be suppressed when M / P contained in the polyester resin which comprises P1 layer exists in the range which satisfy | fills (iii) Formula mentioned above, (DELTA) H tends to become small. Also, regarding the film forming conditions of the polyester film, if a void is formed around the white pigment, the white pigment is likely to slide off from the polyester film. Therefore, if the film is formed so that no void is formed around the white pigment as much as possible, ΔH is small. Tend to be. Details of the film forming conditions will be described later.

Further, the solar cell back surface protection sheet of the present invention preferably has a color tone change Δb ^* of less than 20, more preferably less than 10, even more preferably when the UV treatment test is performed under the above-described ultraviolet treatment conditions. Is less than 5. In the solar cell back surface protection sheet of the present invention, when the color change Δb ^* when the ultraviolet ray treatment test is performed with the P1 layer as the incident surface is 20 or more, the solar cell equipped with the solar cell back surface protection sheet of the present invention is mounted. When installed outdoors for a long period of time, the appearance of the solar cell deteriorates due to color change caused by ultraviolet rays, and the UV deterioration of the polyester resin progresses significantly, causing cracks on the sheet surface due to the decrease in sheet elongation. May lead to. In the solar cell back surface protective sheet of the present invention, the method for setting ΔH to the above range is not particularly limited. For example, Δb ^* can be adjusted by the kind of particles contained in the P1 layer, the M / P contained in the polyester resin constituting the P1 layer, the amount of voids in the P1 layer, and the like. As a type of white pigment, Δb ^* tends to be small when a white pigment having ultraviolet absorbing ability or ultraviolet reflecting ability (light reflectivity) is used. Examples of white pigments having ultraviolet absorbing ability and ultraviolet reflecting ability (light reflectivity) include titanium oxide. Rutile titanium oxide does not promote deterioration of the polyester resin, and therefore tends to reduce Δb ^* . On the other hand, anatase-type titanium oxide tends to increase Δb ^* in order to promote deterioration of the polyester resin. Further, when the M / P contained in the polyester resin constituting the P1 layer is in a range satisfying the above-mentioned formula (iii), decomposition of the polyester resin can be suppressed, and Δb ^* tends to be small. Regarding the film forming conditions of the polyester film, if there is a void in the P1 layer, it has a function of reflecting ultraviolet rays. Therefore, if the film is formed so that a void is formed, Δb ^* tends to be small. Details of the film forming conditions will be described later.

  In addition, the sheet for protecting the back surface of the solar cell of the present invention has a film thickness reduction amount (ΔL) when the treatment for 2000 hours (xenon lamp irradiation test) is performed from the P1 layer side using a xenon lamp irradiation tester under the conditions described later. ) Is preferably 5 μm or less. In the xenon lamp irradiation test, in addition to ultraviolet / visible light irradiation with a xenon lamp, spraying treatment is performed at regular cycle intervals assuming rain and wind stress in an actual environment. This test is an accelerated test of actual outdoor exposure, and corresponds to approximately 20 years of actual outdoor exposure when a solar cell back surface protection sheet is used in a solar cell module. When the film thickness reduction amount (ΔL) is larger than 5 μm, when used in a real environment as a solar cell back surface protection sheet, the insulation property decreases due to the decrease in film thickness, and the solar cell module can withstand the system voltage. May be damaged. A more preferable range is a film thickness reduction amount of 3.5 μm or less, and a further preferable range is 2.5 μm or less.

  As a result of intensive studies on the film thickness reduction of the solar cell back surface protection sheet, the inventors have estimated that the film thickness reduction is caused by the following mechanism. When the sheet for protecting the back surface of the solar cell receives ultraviolet rays contained in sunlight during outdoor exposure, the surface polyester resin decomposes and deteriorates, and the film thickness starts to decrease. This decrease in film thickness is suppressed by exposing the white pigment contained in the solar cell back surface protection sheet to the surface layer and locally increasing the particle concentration on the surface. However, in the outdoor exposure environment, there are external stresses such as rain and wind, and this causes some of the white particles exposed on the surface to flow away, and the film thickness decreases again. There is a difference in the amount of decrease. For this reason, the film thickness reduction amount mainly depends to some extent on the concentration of white particles contained in the solar light exposed surface of the solar cell back surface protection sheet. In addition to the above, it has been clarified through this examination that part of the film forming conditions and the method of preparing the master pellet also contribute partly to the amount of film thickness reduction.

  In the solar cell back surface protection sheet of the present invention, a solar cell back surface protection sheet excellent in powder blowing suppression can be placed outdoors for a long period of time by mounting the solar cell back surface protection sheet of the present invention. A solar cell with low environmental pollution can be obtained. Moreover, in the solar cell back surface protection sheet of the present invention, a solar cell back surface protection sheet of the present invention is placed outdoors for a long period of time by making it a solar cell back surface protection sheet excellent in suppressing color change. However, a solar cell with a small change in appearance can be obtained. Furthermore, in the solar cell back surface protection sheet of the present invention, a solar cell excellent in insulating properties can be obtained even when placed outdoors for a long period of time by simultaneously suppressing the reduction in film thickness.

(Method for producing solar cell back surface protection sheet)
Next, an example is given and demonstrated about the manufacturing method of the solar cell back surface protection sheet | seat of this invention. This is an example, and the present invention should not be construed as being limited to the product obtained by such an example.

  The manufacturing method of the solar cell back surface protection sheet of the present invention can be manufactured by the following method.

  The polyester resin of the present invention can be obtained by using the above-mentioned polymerization catalyst, by transesterifying or esterifying the dicarboxylic acid or its ester derivative and a diol by a known method using the above-mentioned transesterification catalyst. Can do.

  Next, in the case of the P1 layer single film structure which is a weather resistant layer, the manufacturing method of the solar cell back surface protection sheet is a sheet obtained by extruding a P1 layer raw material on a cast drum cooled by a die by heating and melting in an extruder. A method of processing into a shape (melt cast method) can be used. As another method, the raw material for the P1 layer is dissolved in a solvent, and the solution is extruded from a die onto a support such as a cast drum or an endless belt to form a film, and then the solvent is dried and removed from the film layer. A method of processing into a shape (solution casting method) or the like can also be used.

  Moreover, the manufacturing method in the case of the laminated structure which a sheet for solar cell back surface protection consists of a weather-resistant layer (P1 layer) and a base material layer (P2 layer) is a case where the material of each layer to laminate | stack mainly comprises a thermoplastic resin , Preferably using a method (coextrusion method) in which two different thermoplastic resins are put into two extruders, melted and then merged, and co-extruded on a cast drum cooled from a die and processed into a sheet shape Can do.

  Further, when a uniaxial or biaxially stretched sheet base material is selected as a P1 layer monolayer structure and / or a laminate including the P1 layer, as a manufacturing method thereof, first, an extruder (in the case of a laminated structure, a plurality of extruders are used). The raw material is charged into the extruder and melted and extruded from the die (co-extrusion in the case of a laminated structure), and cooled and solidified by static electricity on a cooled drum cooled to a surface temperature of 10 to 60 ° C. An unstretched sheet is produced.

  Next, this unstretched sheet is led to a roll group heated to 70 ° C. or more, stretched in the longitudinal direction (longitudinal direction, that is, the traveling direction of the sheet), and cooled by a roll group having a temperature of 20 to 50 ° C. In the solar cell back surface protection sheet of the present invention, the preferred range of the roll temperature of the stretched portion in the longitudinal direction (hereinafter sometimes referred to as the longitudinal stretch temperature) is 98 ° C. or less. When the temperature exceeds 98 ° C., the crystalline domain of the polyester resin in the sheet grows, and during the subsequent stretching in the tenter, minute voids around the white pigment tend to be generated due to the poor stretchability of the crystal part. A more preferable range is 95 ° C. or lower. The lower limit is not particularly limited as long as the stretchability of the sheet is not impaired, but the glass transition temperature of the polyester resin to be used + 5 ° C. is preferable. Moreover, the preferable range of the draw ratio of the solar cell back surface protection sheet longitudinal direction of this invention is 2.8 times-3.5 times. A more preferable range is 3.0 times to 3.5 times. If the stretching ratio in the longitudinal direction is 2.8 times or less, the formation of minute voids around the white pigment due to stretching can be suppressed, but the change in color tone after the ultraviolet irradiation treatment may increase. This is because the white pigment in an aggregated state in the sheet before stretching is suppressed from being dispersed due to stress during stretching. On the other hand, when the draw ratio exceeds 3.5 times, oriented crystallization of the polyester resin accompanying the drawing proceeds, and the formation of fine voids around the white pigment is promoted starting from the oriented crystallization site having low drawability. And powder blowing worsens.

  Subsequently, the both ends of the sheet are guided to a tenter while being gripped by clips, and are stretched 3 to 4 times in a direction (width direction) perpendicular to the longitudinal direction in an atmosphere heated to a temperature of 80 to 150 ° C. Thereafter, the stretched sheet is heat treated in the tenter after being subjected to stretching relaxation of 1 to 10% in the width direction, thereby stabilizing the internal orientation structure. Here, the heat treatment temperature is preferably in the range of 220 to 250 ° C. By performing the heat treatment, the orientation of the oriented and crystallized polyester resin can be relaxed, and fine voids formed around the white pigment can be filled to suppress powder blowing. This effect becomes more significant at higher temperatures in the aforementioned range. On the other hand, when the temperature is set to 250 ° C. or higher, the relaxation of the orientation crystallization becomes large, and thus the durability of the sheet maintained by the orientation crystallization may be remarkably lowered. Moreover, when the heat treatment is performed at a temperature of less than 220 ° C., the above-mentioned effects cannot be obtained, so that powder blowing deteriorates. On the other hand, the amount of film thickness reduction tends to decrease as the heat treatment temperature is increased. The reason for this phenomenon has not been clarified, but the high-temperature heat treatment increases the proportion of the crystalline structure in which the polyester molecular chains are densely gathered. It is presumed that the reaction will occur and it will be difficult to reduce the molecular weight.

  As the biaxial stretching method, in addition to the sequential biaxial stretching method in which the stretching in the longitudinal direction and the width direction is separated as described above, the simultaneous biaxial stretching method in which the stretching in the longitudinal direction and the width direction is performed simultaneously. Either one does not matter.

(Solar cell)
The solar cell using the solar cell back surface protection sheet of the present invention can have higher durability than the conventional solar cell. An example of the configuration is shown in FIG. A power generating element 3 connected with a lead wire for taking out electricity (not shown in FIG. 1) is sealed with a transparent sealing material 4 such as EVA resin, a transparent substrate 5 such as glass, and a solar cell back surface protection Although it is comprised by bonding together as the sheet | seat 6 (it is comprised by the polyester weather resistance layer 1 (P1 layer) and the polyester base material layer 2 (P2 layer)), it is not limited to this, It can use for arbitrary structures. In addition, in FIG. 1, although the solar cell back surface protection sheet shows an example of a single body, the solar cell back surface protection sheet should be a composite sheet in which other films are laminated according to other required characteristics. Is also possible.

  Here, in the solar cell of the present invention, the solar cell back surface protection sheet plays a role of protecting the power generating element installed on the back surface of the sealing material 4 sealing the power generating element 3. Here, the P2 layer is in contact with the sealing material 4 through a sealing material easy-adhesion layer (not shown in FIG. 1), and the weather-resistant layer P1 layer is the surface layer of the solar cell. It is preferable to arrange so that it comes to. By adopting this configuration, taking advantage of the excellent UV resistance (color change, powder blowing suppression effect) of the present invention, the weather-resistant layer on the surface of the sheet for protecting the back surface of the solar cell is removed for a long time even when exposed to the outdoors. By suppressing the above, it is possible to maintain the protection of the solar battery cells and the prevention of environmental pollution of the solar battery module installation place by the white powder for a long period of time.

  The power generating element 3 converts light energy of sunlight into electric energy, and is based on crystalline silicon, polycrystalline silicon, microcrystalline silicon, amorphous silicon, copper indium selenide, compound semiconductor, dye enhancement Arbitrary elements such as a sensitive system can be used in series or in parallel according to the desired voltage or current depending on the purpose. Since the transparent substrate 5 having translucency is located in the outermost layer of the solar cell, a transparent material having high weather resistance, high contamination resistance, and high mechanical strength characteristics in addition to high transmittance is used. In the solar cell of the present invention, the transparent substrate 5 having translucency can be made of any material as long as the above characteristics are satisfied. Examples thereof include glass, ethylene tetrafluoride-ethylene copolymer (ETFE), polyfluoride. Vinyl fluoride resin (PVF), polyvinylidene fluoride resin (PVDF), polytetrafluoroethylene resin (TFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polytrifluoroethylene chloride resin (CTFE) ), Fluorinated resins such as polyvinylidene fluoride resin, olefinic resins, acrylic resins, and mixtures thereof. In the case of glass, it is more preferable to use a tempered glass. Moreover, when using the resin-made translucent base material, what extended | stretched the said resin uniaxially or biaxially from a viewpoint of mechanical strength is used preferably. Moreover, in order to give these substrates the adhesiveness with EVA resin etc. which are the sealing materials of an electric power generation element, it is also preferably performed to give the surface a corona treatment, a plasma treatment, an ozone treatment, and an easy adhesion treatment. .

  Here, in the solar cell of the present invention, the solar cell back surface protection sheet serves as a reflector that reflects sunlight that has not been absorbed by the power generation element 3. Here, the solar cell back surface protection sheet has good light reflectivity in the P2 layer, so that sunlight is efficiently reflected and a part thereof is incident again on the power generation element 3 to improve the power generation amount of the solar cell. be able to.

  The sealing material 4 for sealing the power generation element is formed by covering and fixing the unevenness of the surface of the power generation element with a resin, protecting the power generation element from the external environment, and having a light-transmitting base material for the purpose of electrical insulation In addition, a material having high transparency, high weather resistance, high adhesion, and high heat resistance is used to adhere to the back surface protection sheet and the power generation element. Examples thereof include ethylene-vinyl acetate copolymer (EVA), ethylene-methyl acrylate copolymer (EMA), ethylene-ethyl acrylate copolymer (EEA) resin, ethylene-methacrylic acid copolymer (EMAA), Ionomer resins, polyvinyl butyral resins, and mixtures thereof are preferably used.

  As described above, by incorporating the solar cell back surface protection sheet of the present invention into a solar cell system, it is possible to reduce changes in appearance as compared with conventional solar cells. The solar cell of the present invention can be suitably used for various applications without being limited to outdoor use and indoor use such as a solar power generation system and a power source for small electronic components.

[Measurement method and evaluation method of characteristics]
(1) Polymer characteristics (1-1) Intrinsic viscosity (IV)
In 100 ml of orthochlorophenol, a measurement sample (polyester resin (raw material) or only the P1 layer of the solar cell back surface protection sheet separated) is dissolved (solution concentration C (measurement sample weight / solution volume) = 1.2 g / 100 ml), the viscosity of the solution at 25 ° C. was measured using an Ostwald viscometer. Similarly, the viscosity of the solvent was measured. [Η] was calculated by the following formula (4) using the obtained solution viscosity and solvent viscosity, and the obtained value was defined as the intrinsic viscosity (IV).
ηsp / C = [η] + K [η] ² · C (4)
(Where ηsp = (solution viscosity / solvent viscosity) −1, K is the Huggins constant (assuming 0.343))
In addition, when there existed insoluble matters, such as inorganic particles, in the solution in which the measurement sample was dissolved, the measurement was performed using the following method.
(I) A measurement sample is dissolved in 100 mL of orthochlorophenol to prepare a solution having a solution concentration higher than 1.2 g / 100 mL. Here, let the weight of the measurement sample used for orthochlorophenol be a measurement sample weight.
(Ii) Next, the solution containing insoluble matter is filtered, and the weight of the insoluble matter is measured and the volume of the filtrate after filtration is measured.
(Iii) Orthochlorophenol was added to the filtrate after filtration, and (measured sample weight (g) −weight of insoluble matter (g)) / (volume of filtrate after filtration (mL) + added orthochlorophenol) The volume (mL) is adjusted to 1.2 g / 100 mL.
(For example, when a concentrated solution having a measurement sample weight of 2.0 g / solution volume of 100 mL was prepared, the weight of insoluble matter when the solution was filtered was 0.2 g, and the filtrate volume after filtration was 99 mL Adjust the addition of 51 mL of orthochlorophenol ((2.0 g-0.2 g) / (99 mL + 51 mL) = 1.2 g / 100 mL))
(Iv) Using the solution obtained in (iii), the viscosity at 25 ° C. is measured using an Ostwald viscometer, and using the obtained solution viscosity and solvent viscosity, η] is calculated, and the obtained value is defined as intrinsic viscosity (IV).

(1-2) Terminal carboxyl group amount (in the table, described as COOH amount)
The terminal carboxyl group amount was measured by the following method according to the method of Malice. (Document M. J. Malice, F. Huizinga, Anal. Chim. Acta, 22 363 (1960)).
2 g of a measurement sample (polyester resin (raw material) or solar cell back surface protection sheet P1 layer only) 2 g was dissolved in 50 ml of o-cresol / chloroform (weight ratio 7/3) at a temperature of 80 ° C. The solution was titrated with a 05N KOH / methanol solution, and the terminal carboxyl group concentration was measured and indicated by the value of equivalent / polyester 1t. In addition, the indicator at the time of titration used phenol red, and the place where it changed from yellowish green to light red was set as the end point of titration. If there is insoluble matter such as inorganic particles in the solution in which the measurement sample is dissolved, the solution is filtered to measure the weight of the insoluble matter, and the value obtained by subtracting the weight of the insoluble matter from the measurement sample weight The following correction was made.

(1-3) Quantitative measurement method of the amount of metal elements excluding the amount of phosphorus and alkali metal elements The amount of elements was measured using a fluorescent X-ray analyzer (model number: 3270) manufactured by Rigaku Corporation.

  8 g of the freeze-ground sample was used as an analysis sample according to the description of JIS K0119. The content of each element in the sample was quantified according to the description of JIS K0119 (1999) 10.1d).

(1-4) Quantitative Measurement Method for Alkaline Metal Amount 1 g of a sample is placed in a platinum dish and completely incinerated at 700 ° C. for 1.5 hours, and then the incinerated product is 0.1 N so that the volume becomes 50 ml. Was dissolved in hydrochloric acid to obtain a solution A. When there was no insoluble matter in the solution A, this was used as a measurement sample.

  On the other hand, when there was an insoluble matter in the solution A, a measurement sample was obtained by the following method. A new sample (1 g) was placed in a platinum dish and completely incinerated at 700 ° C. over 1.5 hours. The incinerated product was then dissolved in 5 ml of 6.5 N nitric acid to obtain a solution B. Solution B was heated and the nitric acid was evaporated to give a residue. This residue was dissolved in 0.1N hydrochloric acid so as to have a volume of 50 ml to obtain a solution B. The solution B was used as a measurement sample.

  Using the above measurement sample, quantification was carried out by atomic absorption spectrometry (manufactured by Tadate Corporation: polarization Zeeman atomic absorption photometer 180-80, frame: acetylene-air). The quantification was performed according to the description of JIS K0121 (1999) 9.1a).

(2) Particle size measurement Using a microtome, a small piece cut in a direction perpendicular to the surface of the solar cell back surface protection sheet was prepared, and the cross section was taken as a field emission scanning electron microscope JSM-6700F (JEOL Ltd.) ) And magnified to 10,000 times. From the cross-sectional photograph, the particle size distribution of particles present in the P1 layer was determined using image analysis software Image-Pro Plus (Nippon Roper Co., Ltd.). The cross-sectional photograph was selected from different arbitrary measurement visual fields, and the equivalent circle diameter of 2500 or more particles arbitrarily selected from the cross-sectional photograph was measured to obtain a number-based average particle diameter.

(3) Constituent element analysis of white pigment JED-2300T (manufactured by JEOL Ltd., Si <Li> semiconductor detector) for the filler observed in the field emission type transmission electron microscope observation by the method described in (2) above , ETW elemental analysis using UTW type) and EELS elemental state analysis using GATAN GIF “Tridiem” to identify the constituent elements of the filler, and to query the obtained EELS spectrum and the EELS spectrum of commercially available metal compounds Thus, the configuration of the filler contained in the P1 layer and the P2 layer was identified.

(4) Content Analysis of White Pigment Only the P1 layer and the P2 layer of the solar cell back surface protection sheet are peeled off, and each is subjected to nitrogen using a thermogravimetric (TGA) apparatus TGA-50 (manufactured by Shimadzu Corporation). The temperature is raised from room temperature to 800 ° C. at a rate of 20 ° C./min under an atmosphere. After the temperature rise, the mass ratio (mass%) of the ash generated after being held at 800 ° C. for 1 hour is measured five times and the average value is calculated. The average value of five measurements of the mass fraction (mass%) of ash obtained by performing the same measurement for a polyester film not containing a filler is obtained. The difference between these two mass fraction average values was determined as the filler concentration (mass%) contained in the P1 layer and the P2 layer.

(5) Thickness of P1 layer and P2 layer Using a microtome, a small piece cut in a direction perpendicular to the surface of the solar cell back surface protection sheet was prepared, and the cross section was taken as a field emission scanning electron microscope JSM-6700F ( JEOL Co., Ltd.) was used to magnify and photograph 10,000 times. The thicknesses of the P1 layer and the P2 layer were calculated from the cross-sectional photograph by reverse calculation from the magnification. In addition, the thickness used the cross-sectional photograph of the total 5 places arbitrarily selected from the different measurement visual field, and used the average value.

(6) Powder blowing evaluation (amount of white powder generated before and after UV treatment test)
(6-1) White powder amount (H value) measurement A sheet for protecting the back surface of a solar cell is attached to the surface of the P1 layer side using Sekisero Tape (registered trademark) No. 252 (manufactured by Sekisui Chemical Co., Ltd., tape width: 15 mm) is pasted and pressed using a 2 kg rubber roller, and then peeled 180 degrees at a speed of 0.12 m / min to 0.18 m / min. Using a fully automatic direct reading haze computer HGM-2DP (manufactured by Suga Test Instruments Co., Ltd.) based on JIS-K7105 (1981), the cellophane tape (registered trademark) from which the sheet for protecting the back surface of the solar cell is peeled off from the P1 layer is used. The haze (%) in the thickness direction of (registered trademark) was measured, and the average of the measured values in three trials was determined as the amount of white powder (H0) on the P1 surface.

(6-2) Amount of white powder generated before and after the ultraviolet treatment test (ΔH)
A sheet for protecting the back surface of the solar cell was placed so that the test light hits the surface on the P1 layer side, and using an i-super ultraviolet tester S-W161 (manufactured by Iwasaki Electric Co., Ltd.), the temperature was 60 ° C., the relative humidity was 50%, Irradiation is performed for 72 hours under conditions of illuminance of 150 mW / cm ² (light source: metal halide lamp, wavelength range: 295 to 450 nm, peak wavelength: 365 nm, conforming to JIS-C-1613). The amount of white powder (H1) on the P1 layer side surface before and after the ultraviolet irradiation test was measured according to the previous section (6-1), and the amount of white powder generated after ultraviolet irradiation (ΔH) was calculated from the following equation (5).
White powder generation after UV irradiation (ΔH) = H1-H0 (5)
H0: Amount of white powder before UV irradiation (H value)
H1: White powder amount (H value) after ultraviolet irradiation.

(7) Yellowing degree (color change before and after UV treatment test)
(7-1) Color tone (b ^* value) measurement Based on JIS-Z-8781-4 (2013), a spectroscopic color difference meter SE-2000 (manufactured by Nippon Denshoku Industries Co., Ltd., light source halogen lamp 12V4A, 0 ° to The color tone (b ^* value) of the P1 layer side surface of the solar cell back surface protection sheet was measured by a reflection method using a -45 ° post-spectral method.

(7-2) Color tone change Δb ^*
The surface on the P1 layer side of the solar cell back surface protection sheet is subjected to the same ultraviolet irradiation test as in the item (6-2), and the color tone (b ^* value) after the test is measured according to the item (7-1). The change in color tone (Δb ^* ) after UV irradiation was calculated from the following equation (6).
Color tone change after UV irradiation (Δb ^* ) = b ^* 1-b ^* 0 (6)
b ^* 0: Color tone before UV irradiation (b ^* value)
b ^* 1: Color tone after UV irradiation (b ^* value).

(8) Appearance change evaluation by outdoor exposure test of solar cell module (8-1) Manufacture of solar cell module Crystal cell type solar cell Q6LPT-G2 manufactured by Qcells, manufactured by HOZAN on the silver electrode part on the back surface Flux H722 is applied with a dispenser, and copper foil SSA-SPS0.2 × 1.5 (20) made by Hitachi Cable is used as a wiring material cut to a length of 155 mm on the front and back silver electrodes. Place the wire 10 mm away from one end of the wire on the end of the wiring material so that the back side is symmetrical to the front side, and use a soldering iron to contact the soldering iron from the back side of the cell and solder the surface and back side simultaneously. 1 cell strings were produced.

  Placed so that the longitudinal direction of the copper foil A-SPS 0.23 × 6.0 made by Hitachi Cable Co., Ltd. is perpendicular to the longitudinal direction of the wiring material protruding from the cell of the produced 1-cell string and the extraction electrode cut into 180 mm, The flux was applied to the portion where the wiring material and the take-out electrode overlapped, and solder welding was performed to produce strings with the take-out electrode.

  Next, 190 mm × 190 mm 3.2 mm thick white plate heat-treated glass for solar cells manufactured by Asahi Glass Co., Ltd., 190 mm × 190 mm 500 μm thick EVA sheet (vinyl acetate copolymerization ratio: 28 mol%), prepared strings with extraction electrodes, 190 mm × A 190 mm 500 μm thick EVA sheet and a solar cell back surface protection sheet cut out to 190 mm × 190 mm are stacked in order so that the P2 layer side surface is located on the EVA side, and the glass is brought into contact with the hot platen of the vacuum laminator Then, vacuum laminating was performed under the conditions of a hot platen temperature of 145 ° C., vacuuming for 4 minutes, pressing for 1 minute, and holding time of 10 minutes. At this time, the strings with extraction electrodes were set so that the glass surface was on the cell surface side.

(8-2) Outdoor actual exposure test Under an environment with a solar irradiation amount of 270 MJ / m ² (wavelength: 280 nm to 400 nm) (Otsu City, Shiga Prefecture), a stand installed at an inclination angle of 35 degrees southward (8- 1) The solar cell module described above is installed so that sunlight directly hits the P1 layer, and a 6-month actual outdoor exposure test is performed, so that the amount of white powder generated in the solar cell module (ΔH) and the change in color tone (Δb ^* ) The two items were evaluated.

(9) Amount of white powder before and after the actual outdoor exposure test The amount of white powder (H value) of the module before the solar cell before and after the actual outdoor exposure described in the previous section (8-2) is measured according to the above (6-2), The white powder generation amount (ΔH) was calculated from the following equation (7).
Amount of 6 white powder generated after UV irradiation (ΔH) = H1 (actual exposure) −H0 (actual exposure) (7)
H0 (actual exposure): White powder quantity before outdoor actual exposure test (H value)
H1 (actual exposure): amount of white powder before outdoor actual exposure test (H value)
From the obtained white powder generation amount (ΔH), the following was determined with respect to the powder blowing of the solar cell module of the solar cell back surface protection sheet.
When the amount of white powder (ΔH) is 4% or more and 15% or less: A
When the amount of white powder (ΔH) is greater than 15% and less than 20%: B
When the white powder generation amount (ΔH) is greater than 20% and 25% or less: C
When the amount of white powder generated (ΔH) is less than 4% or greater than 25%: D
As for the appearance change regarding the glossiness of the solar cell module, A to C are good, and A is the best among them.

(10) Color change Δb ^* before and after the actual outdoor exposure test
The color tone (b ^* value) of the module before the solar cell before and after the actual outdoor exposure described in the previous item (8-2) is measured in accordance with the item (7-2), and the color tone change after ultraviolet irradiation is calculated from the following equation (8). (Δb ^* ) was calculated.
Color tone change after UV irradiation (Δb ^* ) = b ^* 1 (actual exposure) −b ^* 0 (actual exposure) (8)
b0 (actual exposure): Color tone before the actual outdoor exposure test (b ^* value)
b1 (actual exposure): Color after outdoor exposure test (b ^* value)
From the obtained color tone change (Δb ^* ), the solar cell module color tone change of the solar cell back surface protection sheet was determined as follows.
When the color change (Δb ^* ) is less than 1.5: A
When the color change (Δb ^* ) is 1.5 or more and less than 3.5: B
When the color change (Δb ^* ) is 3.5 or more and less than 7.5: C
When color change (Δb ^* ) is 7.5 or more: D
As for the external appearance change regarding the color tone of the solar cell module, A to C are good, and A is the best among them.

(11) Formability of sheet The moldability during production of the solar cell back surface protection sheet of the present invention was evaluated as follows.
Sheets can be formed without problems: A
Sheet breakage occurs once in a 5000m film formation: B
Sheet breakage occurs once in 2000m film formation: C
Sheet breakage occurs once in 500m film formation: D
As for the moldability of the solar cell back surface protective sheet, A to C are good, and A is the best among them.

(12) Reduced film thickness (ΔL)
(12-1) Xenon lamp irradiation test Super xenon in which a solar cell back surface protection sheet is placed so that the test light strikes the surface on the P1 layer side, and a quartz glass filter is mounted on the inner side and a daylight filter is mounted on the outer side. Using a weather meter (manufactured by Suga Test Instruments Co., Ltd.), JIS-K-7350-2 (2008) compliant, irradiation intensity 180 W / m ² (300-400 nm), temperature (black panel temperature) 63 ° C., The xenon lamp irradiation test is performed for 2000 hours under the condition of 50% relative humidity. In this test, a cycle (one cycle 120 minutes) in which the spraying process using the spray device built in the apparatus is performed every 102 minutes for 18 minutes while continuing the xenon lamp irradiation is repeated 1000 times.

(12-2) Film thickness measurement The solar cell back surface protection sheet is cut into a rectangle 6 cm long and 7 cm wide. Measure the thickness of a total of 5 points at the center of the rectangular sample, 4 points 1.5 cm away from the center, 2 cm away from the center, and protect the back of the solar cell. The thickness of the sheet.

(12-3) Film thickness reduction amount ΔL
Let the thickness of the solar cell back surface protection sheet obtained in the preceding item (12-2) be the sheet thickness (L0) before the xenon lamp irradiation test. The xenon lamp irradiation test (2000 hours) described in the previous section (12-1) was performed on the rectangular sample used in (12-2) above, and the xenon lamp irradiation measured by the method described in the previous section (12-1). The thickness after the test is defined as the sheet thickness (L1) after the xenon lamp irradiation test. Using L0 and L1, ΔL calculated using the following equation (9) was defined as the film thickness reduction amount.
Film thickness reduction amount (ΔL) = L1-L0 (9)
(13) Long-term insulation evaluation (13-1) Partial discharge voltage measurement Under the IEC 60664 / A2: 2002 standard, the P1 layer side is the upper measurement surface of the solar cell back surface protection sheet cut into a size of 50 mm × 50 mm. As a partial discharge voltage test apparatus “KPD2050” (manufactured by Kikusui Electronics Co., Ltd.), a partial discharge voltage test was conducted under the following conditions.
Maximum voltage: 1.6KV
Frequency: 50Hz
Test time: 22.0s
Test pattern: Ramp (step-up 10.0 s, maximum voltage holding 2.0 s, step-down 10.0 s)
Pulse detection method and level: + 50%
Extinction voltage measurement charge: 50pC
Measurement was performed on five different cut samples, and the average value of the extinction voltage (V) obtained in the test was defined as the partial discharge voltage (V0) of the solar cell back surface protection sheet.

(13-2) Partial discharge voltage after actual outdoor exposure The sunlight used for the P1 layer side of the solar cell back surface protection sheet is directly applied to the mount used in the actual outdoor exposure test described in (8-2) above. After the installation, a two-year outdoor exposure test was conducted. The partial discharge voltage (V1) was calculated | required like the previous clause (13-1) for the solar cell back surface protection sheet after a test.

(13-3) Partial discharge voltage drop amount ΔV
The partial discharge voltage (V0) of the solar cell back surface protection sheet obtained in the previous item (13-1), and the partial discharge voltage (V1) of the solar cell back surface protection sheet after the outdoor actual exposure test determined in the previous item (13-1). The partial discharge voltage drop amount (ΔV) obtained by the following formula (10) was obtained. Partial discharge voltage drop amount (ΔV) = V1-V0 (10)
From the numerical value of ΔV, the long-term insulation of the solar cell back surface protection sheet was evaluated as follows.
Partial discharge voltage drop (ΔV) is 0V or more and less than 6V: A
Partial discharge voltage drop (ΔV) is 6V or more and less than 8.5V: B
Partial discharge voltage drop (ΔV) is 8.5 V or more and less than 15 V: C
Partial discharge voltage drop (ΔV) is 15 V or more: D
As for the long-term insulation of the solar cell back surface protection sheet, A to C are good, and A is the best among them.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated, this invention is not necessarily limited to these.
(Polyester resin raw material)
1. PET raw material 1 (used in Examples 1 to 14 and Comparative Examples 1 to 6)
100 parts by mass of dimethyl terephthalate, 57.5 parts by mass of ethylene glycol, 0.065 parts by mass of manganese acetate (2.91 mol / t in terms of Mn metal element), 0.03 parts by mass of antimony trioxide at 150 ° C. in a nitrogen atmosphere And melted. While stirring this melt, the temperature was raised to 230 ° C. over 3 hours to distill methanol, and the transesterification reaction was completed. After the transesterification reaction, 0.012 parts by mass of phosphoric acid (equivalent to 1.25 mol / t) and 0.027 parts by mass of sodium dihydrogen phosphate dihydrate (equivalent to 1.65 mol / t) were mixed with 0.5% ethylene glycol. An ethylene glycol solution (pH 5.0) dissolved in parts by mass was added. The intrinsic viscosity of the polyester composition at this time was less than 0.2. Thereafter, the polymerization reaction was carried out at a final temperature of 285 ° C. and a degree of vacuum of 0.1 Torr. / T polyethylene terephthalate was obtained. 160 of the obtained polyethylene terephthalate
Dry and crystallize at 6 ° C. for 6 hours. Thereafter, solid phase polymerization was performed at 220 ° C. and a vacuum degree of 0.3 Torr for 8 hours. / T polyethylene terephthalate (PET-1) was obtained. The obtained polyethylene terephthalate composition had a glass transition temperature of 82 ° C. and a melting point of 255 ° C.

2. PET raw material 2 (used in Comparative Example 7)
The above 1. except that 100 parts by mass of terephthalic acid is used as the dicarboxylic acid component, 100 parts by mass of ethylene glycol is used as the diol component, and manganese acetate, antimony trioxide and phosphorous acid are used as the catalyst. The intrinsic viscosity is 0.80 and the COOH end group amount is 10 eq. / T polyethylene terephthalate (PET-2) was obtained. The obtained polyethylene terephthalate composition had a glass transition temperature of 82 ° C. and a melting point of 255 ° C.

3. PET raw material 3 (used in Examples 1 to 14 and Comparative Examples 1 to 7)
The above 1. except that 100 parts by mass of terephthalic acid is used as the dicarboxylic acid component, 100 parts by mass of ethylene glycol is used as the diol component, and magnesium acetate, antimony trioxide and phosphorous acid are used as the catalyst. The intrinsic viscosity is 0.70 and the COOH end group amount is 300 eq. / T polyethylene terephthalate (PET-3) was obtained. The obtained polyethylene terephthalate composition had a glass transition temperature of 82 ° C. and a melting point of 255 ° C.

4). PET-1 raw material-based titanium oxide A master (used in Examples 1 to 12 and Comparative Examples 1 to 5 and 7)
Above 1. In a biaxial extruder at 290 ° C. in which 100 parts by mass of the PET resin (PET-1) obtained by the above item and 25 parts by mass of rutile titanium oxide A (TiO ₂ -A) having an average particle diameter of 0.210 μm were vented ( The mixture was melt-kneaded with a screw (diameter: 45 mm, rotation speed: 200 rpm) to prepare a 20% by mass titanium oxide master pellet. Thereafter, 100 parts by mass of 20% by mass titanium oxide master pellets and 60 parts by mass of titanium particles A (TiO ₂ -A) were melt-kneaded again in a twin screw extruder (screw: 45 mm diameter, rotation speed: 200 rpm), and 50 masses. % PET-1 raw material base titanium oxide A master pellet (PET-TiO ₂ (1A)) was obtained.

5. PET-1 raw material-based titanium oxide B master (used in Example 13)
The above 4. except that rutile type titanium oxide particles B (TiO ₂ -B) having an average particle size of 0.090 μm were used. 50 mass% PET-1 raw material base titanium oxide B master pellet (PET-TiO ₂ (1B)) was obtained by the method described in the section.

6). PET-1 raw material-based titanium oxide C master (used in Example 14)
4. The above except that rutile type titanium oxide particles C (TiO ₂ —C) having an average particle size of 0.270 μm were used. 50 mass% PET-1 raw material base titanium oxide C master pellet (PET-TiO ₂ (1D)) was obtained by the method described in the section.

7). PET-1 raw material-based titanium oxide D master (used in Comparative Example 6)
The above 4. except that rutile type titanium oxide particles D (TiO ₂ -D) having an average particle size of 0.290 μm were used. 50 mass% PET-1 raw material base titanium oxide C master pellet (PET-TiO ₂ (1D)) was obtained by the method described in the section.

8). PET-2 raw material-based titanium oxide A master (used in Comparative Example 7)
2. 4 except that the PET resin (PET-2) obtained according to the above item and rutile titanium oxide A (TiO ₂ -A) having an average particle size of 0.210 μm were used. 50 mass% PET-1 raw material base titanium oxide A master pellet (PET-TiO ₂ (2A)) was obtained by the method described in the section.

(Examples 1-12)
PET raw material (PET-1) vacuum-dried at 180 ° C. for 2 hours and PET-1 raw material-based titanium oxide A master pellet (PET-TiO ₂ (1A)) were vacuum-dried at 180 ° C. for 2 hours using the P1 layer raw material. Using PET raw material (PET-3) and PET-1 raw material-based titanium oxide A master pellet (PET-TiO ₂ (1A)) as a P2 layer raw material, the amount of particles is adjusted to the concentration shown in Table 1 and extruded at 280 ° C. It was melt-kneaded in the machine and introduced into the T die die. Subsequently, it was melt-extruded into a sheet form from a T-die die and adhered and cooled and solidified by an electrostatic application method on a drum maintained at a surface temperature of 25 ° C. to obtain an unstretched sheet. Subsequently, after preheating the unstretched sheet with a roll group heated to a temperature of 80 ° C., between the roll heated to the “longitudinal stretching temperature (° C.)” shown in Table 1 and the roll adjusted to a temperature of 25 ° C. After stretching in the longitudinal direction (longitudinal direction) at the “longitudinal stretching ratio (times)” described in Table 1, cooling with a roll group at a temperature of 25 ° C. to obtain a uniaxially stretched sheet It was.

  While holding both ends of the obtained uniaxially stretched sheet with a clip, the tenter is guided to a preheating zone at a temperature of 80 ° C. in the tenter, and then continuously heated at 90 ° C. in a direction perpendicular to the longitudinal direction (width direction). The film was stretched 3.75 times. Subsequently, heat treatment was performed for 20 seconds at the “heat treatment temperature (° C.)” shown in Table 1 in the heat treatment zone in the tenter, and further, relaxation treatment was performed in the 4% width direction under the same temperature condition. Then, it was gradually cooled gradually to form a sheet having a total thickness of 150 μm. When the properties of the obtained sheet were evaluated, the intrinsic viscosity (IV), the amount of terminal carboxyl groups, the thickness of the sheet, the amount of elements contained in the P1 layer, and the average particle size of the white pigment contained in the P1 layer determined by observing the cross section of the P1 layer The diameter and the constituent elements of the white pigment were as shown in Tables 1 and 2.

About the obtained solar cell back surface protection sheet, characteristic evaluation as a solar cell back surface protection sheet and solar cell module characteristic evaluation were performed. As shown in Tables 2 and 3, the results are shown in Tables 1 and 2. In Examples 1 to 12, the P1 layer is composed of titanium oxide (detection elements: Ti, O) having an average particle size in the range of 0.1 μm or more and less than 0.30 μm. The white pigment is contained at a concentration ranging from 6% by mass to 13% by mass, and the content P (mol / t) of the phosphorus element contained in the P1 layer is 1.8 mol / t with respect to the entire polyester resin. t or more and 5.0 mol / t or less, containing at least one metal element of Mn and Ca, and the content of divalent metal elements other than Mn and Ca is 5 ppm with respect to the whole polyester resin, respectively. The content of the alkali metal element with respect to the whole polyester resin is M1 (mol / t), and the total of the Mn element content and the Ca element content with respect to the whole polyester resin is M2 ( mol / t), the value M / P when the metal content M (mol / t) in the polyester resin is divided by the phosphorus element content P (mol / t) is 1.0 or more. It was confirmed that it was 0 or less. Moreover, all of these Examples 1-12 confirmed that white powder generation amount (DELTA) H after an ultraviolet irradiation treatment test was 5% or more and 30% or less. In particular, in Example 1, the white powder generation amount ΔH, the color tone change Δb ^* , and the film thickness reduction amount ΔL before and after the ultraviolet ray treatment test are good, and at the same time, the sheet formability is also good. It was confirmed that the solar cell module had a good effect of suppressing powder blowing and color change after the outdoor actual exposure test and was excellent in long-term insulation.

As the film forming conditions of the back surface protection sheet for solar cells, when the longitudinal stretching ratio is changed to 2.8 times (Example 3) and 3.5 times (Example 2), it is directly proportional to the increase of the stretching ratio. It was confirmed that the color tone change Δb ^* before and after the UV treatment test decreased and the white powder generation amount ΔH tended to increase. For this reason, in (Example 3), the solar cell module using the solar cell back surface protection sheet has the effect of suppressing color change after the outdoor actual exposure test, and in (Example 2), the solar cell back surface protection sheet is used. The solar cell module confirmed that the powder blowing suppression effect after an outdoor real exposure test fell. This is because, as the draw ratio increases, the dispersion of titanium oxide, which is a white pigment, is improved, while more fine voids are generated around the titanium oxide and the generation of white powder is increased. When the longitudinal stretching temperature is changed to 98 ° C. (Example 4), the white powder generation amount ΔH before and after the UV treatment test tends to increase, and the solar cell module using the solar cell back surface protection sheet is exposed outdoors. It was confirmed that the powder blowing effect after the test was lowered. This is because the crystallization in the sheet progresses due to the increase in the stretching temperature, and then the stretching in the tenter is performed. As the crystallization site increases, the stretchability decreases and fine voids are formed around the titanium oxide particles. it is conceivable that. Furthermore, it was confirmed that when the heat treatment temperature was increased to 250 ° C., the amount of white powder generated was as good as or higher than that in Example 1. This is considered to be because minute voids formed during stretching by heat treatment can be crushed by slight melting and orientation relaxation in the biaxially stretched polyester resin.

Regarding the titanium oxide concentration in the P1 layer, it was confirmed that when the amount was increased to 13% by mass (Example 6), the amount of white oxide generated increased as the number of titanium oxide particles serving as the starting point of white powder generation increased. On the other hand, when the amount of titanium oxide added to the P1 layer is reduced to 6% by mass (Example 8), the white powder generation amount ΔH decreases with a decrease in the number of titanium oxide particles, while the amount of titanium oxide in the P1 layer due to titanium oxide decreases. The change in color tone Δb ^* increases due to a decrease in UV absorption efficiency, and the decrease in the number of titanium oxide particles increases the amount of surface polyester resin that deteriorates before the UV hiding property is obtained. It was confirmed that there is a tendency to increase.

  When the combination with the above-mentioned stretching conditions was carried out, the white powder generation amount ΔH was obtained when the titanium oxide concentration of the P1 layer was changed to 13% by mass and the longitudinal stretching ratio was changed to 3.5 times (Example 7). In the case of changing the titanium oxide concentration to 6% by mass, the draw ratio to 2.8 times, and the heat treatment temperature to 250 ° C. (Example 9), the white powder generation amount ΔH is 5% which is the minimum in the present invention. It became. Further, it was confirmed that the crystal structure in the film was promoted by increasing the heat treatment temperature, and the film thickness reduction amount ΔL tended to decrease as the deterioration rate of the polyester resin slowed down.

When the P1 layer ratio in the solar cell back surface protection sheet is changed to 10% (Example 10), although the color change Δb ^* is increased due to an increase in the ultraviolet transmittance of the P1 layer, the amount of white powder generated ΔH is an example. It was confirmed to be as good as 1. On the other hand, when the P1 stacking ratio is changed to 30% (Example 11) and 100% (Example 12), the moldability of the solar cell back surface protection sheet decreases and the productivity deteriorates as the P1 layer ratio increases. However, it was confirmed that the white powder generation amount ΔH was as good as in Example 1.

(Examples 13 and 14)
In Example 13, instead of PET-1 raw material-based titanium oxide A master pellet (PET-TiO ₂ (1A)), PET-1 raw material-based titanium oxide B master pellet (PET-TiO ₂ (1B)) was used. 14 was carried out except that PET-1 raw material-based titanium oxide C master pellet (PET-TiO ₂ (1C)) was used instead of PET-1 raw material-based titanium oxide A master pellet (PET-TiO ₂ (1A)). A sheet was obtained in the same manner as in Example 1.
Example 1 except that PET-1 raw material-based titanium oxide C master pellet (PET-TiO ₂ (1C)) was used instead of PET-1 raw material-based titanium oxide A master pellet (PET-TiO ₂ (1A)) Similarly, a sheet was obtained. When the properties of the obtained sheet were evaluated, the intrinsic viscosity (IV), the amount of terminal carboxyl groups, the thickness of the sheet, the amount of elements contained in the P1 layer, and the average particle size of the white pigment contained in the P1 layer determined by observing the cross section of the P1 layer The diameter and the constituent elements of the white pigment were as shown in Tables 1 and 2.

  About the obtained solar cell back surface protection sheet, characteristic evaluation as a solar cell back surface protection sheet and solar cell module characteristic evaluation were performed. As shown in Tables 2 and 3, when the average particle diameter of titanium oxide is changed to 0.10 μm (Example 13), the white powder generation amount ΔH and the film thickness reduction amount ΔL are increased by the increase in the photocatalytic activity of titanium oxide. Confirmed to rise. Further, when the average particle diameter of titanium oxide is changed to 0.29 μm (Example 14), the number of titanium oxide particles present in the P1 layer decreases, but the size of voids generated during stretching increases. It confirmed that white powder generation amount (DELTA) H rose as a result.

(Comparative Examples 1-4)
PET raw material (PET-1) vacuum-dried at 180 ° C. for 2 hours and PET-1 raw material-based titanium oxide A master pellet (PET-TiO ₂ (1A)) were vacuum-dried at 180 ° C. for 2 hours using the P1 layer raw material. Using PET raw material (PET-3) and PET-1 raw material-based titanium oxide A master pellet (PET-TiO ₂ (1A)) as the P2 layer raw material, the titanium oxide content and film forming conditions are as shown in Table 1. A sheet was obtained in the same manner as in Example 1 except for the change. When the properties of the obtained sheet were evaluated, the intrinsic viscosity (IV), the amount of terminal carboxyl groups, the thickness of the sheet, the amount of elements contained in the P1 layer, and the average particle size of the white pigment contained in the P1 layer determined by observing the cross section of the P1 layer The diameter and the constituent elements of the white pigment were as shown in Tables 1 and 2.
About the obtained solar cell back surface protection sheet, characteristic evaluation as a solar cell back surface protection sheet and solar cell module characteristic evaluation were performed. The results are shown in Tables 2 and 3. As shown in Tables 2 and 3, the longitudinal stretching ratio (Comparative Example 1), the longitudinal stretching temperature (Comparative Example 2), the heat treatment temperature (Comparative Example 3), and the titanium oxide-containing concentration in the P1 layer (Comparative Example 4). ) Deviates from the preferred range, the amount of white powder ΔH after the ultraviolet irradiation treatment of the film is remarkably reduced, and the solar cell module using the solar cell back surface protection sheet exhibits powder blowing and color change after the outdoor actual exposure test. It was confirmed that the suppression effect was significantly reduced. Further, in Comparative Example 4, it was confirmed that the long-term insulation decreased with the decrease in the film thickness reduction amount ΔL when the heat treatment temperature was lowered.

(Comparative Example 5)
PET raw material (PET-1) vacuum-dried at 180 ° C. for 2 hours and PET-1 raw material-based titanium oxide A master pellet (PET-TiO ₂ (1A)) were vacuum-dried at 180 ° C. for 2 hours using the P1 layer raw material. Using PET raw material (PET-3) and PET-1 raw material-based titanium oxide A master pellet (PET-TiO ₂ (1A)) as the P2 layer raw material, the titanium oxide content and film forming conditions are as shown in Table 1. A sheet was obtained in the same manner as in Example 1 except for the change. When the properties of the obtained sheet were evaluated, the intrinsic viscosity (IV), the amount of terminal carboxyl groups, the thickness of the sheet, the amount of elements contained in the P1 layer, and the average particle size of the white pigment contained in the P1 layer determined by observing the cross section of the P1 layer The diameter and the constituent elements of the white pigment were as shown in Tables 1 and 2.
About the obtained solar cell back surface protection sheet, characteristic evaluation as a solar cell back surface protection sheet and solar cell module characteristic evaluation were performed. The results are shown in Tables 2 and 3, when the titanium oxide-containing concentration of the P1 layer (Comparative Example 4) deviates from the lower limit of the preferred range, the white powder generation amount ΔH after the ultraviolet irradiation treatment of the film is out of the lower limit range, Although the powder blowing can be suppressed, the color tone change Δb ^* is remarkably deteriorated, and it is difficult for the solar cell module using the solar cell back surface protection sheet to achieve both the powder blowing after the outdoor actual exposure test and the suppression effect of the color tone. It was confirmed that Furthermore, in the solar cell module using the solar cell back surface protection sheet, it was found that cracks were confirmed on the sheet surface after the outdoor actual exposure test, and the long-term insulation was significantly reduced.

(Comparative Example 6)
Example 1 except that PET-1 raw material-based titanium oxide D master pellet (PET-TiO ₂ (1D)) was used instead of PET-1 raw material-based titanium oxide A master pellet (PET-TiO ₂ (1A)) Similarly, a sheet was obtained. When the properties of the obtained sheet were evaluated, the intrinsic viscosity (IV), the amount of terminal carboxyl groups, the thickness of the sheet, the amount of elements contained in the P1 layer, and the average particle size of the white pigment contained in the P1 layer determined by observing the cross section of the P1 layer The diameter and the constituent elements of the white pigment were as shown in Tables 1 and 2.
About the obtained solar cell back surface protection sheet, characteristic evaluation as a solar cell back surface protection sheet and solar cell module characteristic evaluation were performed. The results are as shown in Tables 2 and 3. When the average particle diameter of titanium oxide contained in the P1 layer becomes 0.3 μm, the amount of white powder ΔH after the ultraviolet irradiation treatment of the solar cell back surface protection sheet significantly increases. And the solar cell module using this solar cell back surface protection sheet confirmed that the inhibitory effect of the powder blowing and color tone change after an outdoor real exposure test fell remarkably.

(Comparative Example 7)
Example 1 except that PET-2 raw material base titanium oxide A master pellet (PET-TiO ₂ (2A)) was used instead of PET-1 raw material base titanium oxide A master pellet (PET-TiO ₂ (1A)) Similarly, a sheet was obtained. When the properties of the obtained sheet were evaluated, the intrinsic viscosity (IV), the amount of terminal carboxyl groups, the thickness of the sheet, the amount of elements contained in the P1 layer, and the average particle size of the white pigment contained in the P1 layer determined by observing the cross section of the P1 layer The diameter and the constituent elements of the white pigment were as shown in Tables 1 and 2.
About the obtained solar cell back surface protection sheet, characteristic evaluation as a solar cell back surface protection sheet and solar cell module characteristic evaluation were performed. The results are as shown in Tables 2 and 3, and the M / P, which is the ratio of the phosphorus element content and the metal element content in the polyester resin constituting the P1 layer, deviates from the preferred range, so that the back surface of the solar cell The white powder generation amount ΔH after the ultraviolet ray irradiation treatment of the protective sheet is remarkably increased, and the solar cell module using the solar cell back surface protective sheet significantly reduces the effect of suppressing powder blowing and color change after the outdoor actual exposure test. It was confirmed. Moreover, it was confirmed that long-term insulation deteriorates. This was presumed to be due to a decrease in the dispersibility of titanium oxide in the master pellet.

  The solar cell back surface protection sheet of the present invention can greatly suppress the white pigment falling off (powder blowing) accompanying the decomposition of the polyester resin surface even after the ultraviolet irradiation treatment test for decomposing the polyester resin. Therefore, by using the sheet, it is possible to suppress the lack of weather resistance due to the powder blowing of solar cells and induce environmental pollution in the outdoor environment where sunlight including ultraviolet rays that decompose the polyester resin falls strongly. Can be provided.

1. P1 layer2. P2 layer3. Power generation element 4. 4. Sealing material Transparent substrate6. Photovoltaic battery back surface protection sheet

Claims (7)

A sheet for protecting a back surface of a solar cell, which has a layer (P1 layer) having a polyester resin as a main constituent component on at least one surface layer and satisfies the following (1).
(1) The P1 layer surface was subjected to a tape peeling test under the following conditions, and the peeled tape was measured with a haze meter under the following conditions, the haze value was H0, and the P1 layer surface was subjected to ultraviolet irradiation treatment under the following conditions. When the haze value is H1 when the tape peel test was conducted later under the following conditions and the peeled tape was measured with a haze meter under the following conditions, ΔH represented by the formula (i) is 5% or more and 30% or less. There is.
Formula (i) (DELTA) H = H1-H0
<< Tape peeling test conditions >>
On the P1 layer side surface of the solar cell back surface protective sheet, 252 (manufactured by Sekisui Chemical Co., Ltd., tape width: 15 mm) is pasted and pressed using a 2 kg rubber roller, and then peeled 180 degrees at a speed of 0.12 m / min to 0.18 m / min.
<< Haze measurement conditions >>
Using the fully automatic direct reading haze computer HGM-2DP (manufactured by Suga Test Instruments Co., Ltd.) based on JIS-K7105 (1981), the haze (%) in the thickness direction of the cello tape is measured on the Sekisui Cello tape peeled from the P1 layer. taking measurement. The average of the three measurements is taken as the haze value.
<Ultraviolet irradiation treatment conditions>
Installed so that the test light hits the surface on the P1 layer side of the solar cell back surface protection sheet, using an i-super ultraviolet tester S-W161 (manufactured by Iwasaki Electric Co., Ltd.), temperature 60 ° C., relative humidity 50 R%, Irradiation is performed for 72 hours under conditions of illuminance of 150 mW / cm ² (light source: metal halide lamp, wavelength range: 295 to 450 nm, peak wavelength: 365 nm, conforming to JIS-C-1613). The polyester resin and P2 layer which have adjacently the layer (P1 layer) which has the said polyester resin as a main component, and the base material layer (P2 layer) which has a polyester resin as a main component are adjacent. 2. The back surface of a solar cell according to claim 1, wherein both of the polyester resins constituting the white resin contain a white pigment, and the white pigment content of the polyester resin constituting the P1 layer is 6% by mass or more and 13% by mass or less. Protective sheet. The thickness of the said P1 layer is 10% or more and 30% or less with respect to the total thickness of the said P1 layer and the said P2 layer, The solar cell back surface protection sheet of Claim 2 characterized by the above-mentioned. 3. The solar cell according to claim 2, wherein the white pigment contained in each of the P1 layer and the P2 layer is titanium oxide, and the number average particle diameter thereof is 0.1 μm or more and less than 0.3 μm. Back protection sheet. 4. The polyester resin composition constituting the P1 layer contains phosphoric acid and an alkali metal phosphate, and the phosphorus element content P (mol / t) is 1.8 mol / t or more to the entire polyester resin. 0 mol / t or less, containing at least one kind of metal element of Mn and Ca, and the content of divalent metal elements other than Mn and Ca is 5 ppm or less with respect to the whole polyester resin, When the content of the alkali metal element with respect to the entire polyester resin is M1 (mol / t) and the total of the Mn element content and the Ca element content with respect to the entire polyester resin is M2 (mol / t), the following (ii) ), The metal content M (mol / t) in the polyester resin and the content P (mol / t) of the phosphorus element are as follows: i) a solar cell back surface protective sheet according to claim 2, characterized in that satisfies the equation.
Formula (ii) M = M1 / 2 + M2
Formula (iii) 1.1 ≦ M / P ≦ 3.0 6. The back surface of a solar cell according to claim 1, wherein the P1 layer surface has a film thickness reduction amount (ΔL) of 5 μm or less when a xenon lamp irradiation test is performed for 2000 hours under the following conditions. Protective sheet.
<Xenon lamp irradiation test conditions>
A super xenon weather meter (Suga Test Instruments Co., Ltd.) with a solar cell back surface protection sheet installed so that the test light hits the P1 layer side surface, and a quartz glass filter as the filter and a daylight filter as the outer Xenon lamp under the conditions of irradiation intensity of 180 W / m ² (300-400 nm), temperature (black panel temperature) of 63 ° C., and relative humidity of 50% in accordance with JIS-K-7350-2 (2008). The irradiation test is performed for 2000 hours. In this test, a cycle (one cycle 120 minutes) in which the spraying process using the spray device built in the apparatus is performed every 102 minutes for 18 minutes while continuing the xenon lamp irradiation is repeated 1000 times.
<< Measurement conditions for film thickness reduction >>
A sheet for protecting the back surface of the solar cell is cut into a rectangle 6 cm long and 7 cm wide. Measure the thickness of a total of 5 points with a thickness meter at the center of the rectangular sample and 4 points 1.5 cm in the vertical direction and 2 cm in the horizontal direction, and average the thickness of these 5 points to the xenon lamp irradiation test The previous sheet thickness (L0) is used.
The rectangular sample is subjected to the above xenon lamp irradiation test for 2000 hours, and then the sheet thickness is measured by the same method as described above, and the obtained value is defined as the sheet thickness (L1) after the xenon lamp irradiation test. Using L0 and L1, the film thickness reduction amount (ΔL) is obtained from the following equation (9).
Film thickness reduction amount (ΔL) = L1-L0 (9) A solar cell module comprising the solar cell back surface protection sheet according to claim 1.

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