TW201544321A - Polyester film for solar cell back plates - Google Patents

Abstract

The present invention relates to a polyester film for solar cell back plates, which has at least a surface layer comprising a polyester film satisfying the following conditions (1)-(3) (the layer being referred to as a P1 layer). (1) The P1 layer has a thickness that is greater than 30[mu]m and less than 250 [mu]m. (2) Surface roughness (Ra) of the P1 layer is greater than 0.10 [mu]m and less than 0.50 [mu]m. (3) The amount of reduction of the thickness of the P1 layer after an endurance test is less than 15 [mu]m and an elongate rate is maintained greater than 40%. The present invention provides a polyester film, which, even if being used outdoors for an extended period of time, shows a less amount of thickness reduction and reduced lowering of humidity/heat resistance, weather resistance, and electrical insulation.

Description

Polyester film for solar battery back sheet

The present invention relates to a polyester film for a solar cell back sheet, which has a small reduction in thickness of a film even when used outdoors for a long period of time, and has a small reduction in moisture heat resistance, weather resistance, and electrical insulation.

Polyester film is used for magnetic recording media, electrical insulation, solar cells, capacitors, packaging, and various industrial applications due to its excellent mechanical properties, thermal properties, electrical properties, surface properties, and heat resistance. Materials and other uses.

In recent years, solar cells, which are clean energy sources, are rapidly spreading as a new generation of energy that is semi-permanent and pollution-free. The solar cell is obtained by sealing a transparent substrate such as glass with a transparent sealing material such as an ethylene-vinyl acetate copolymer (hereinafter sometimes referred to as EVA), and a resin called a solar cell back sheet. Made up of plates. The sunlight is introduced into the solar cell through the transparent substrate. The sunlight introduced into the solar cell is absorbed by the power generating element, and the absorbed light energy is converted into electric energy. The converted electrical energy is extracted from the leads connected to the power generating components for use in various electrical equipment. Here, the solar cell back sheet is used for the purpose of protecting the power generating element of the solar cell from external influences such as rain. Polyester film is used as a solar cell backsheet or as a component of the backsheet due to its excellent properties.

The solar cell is placed on the outdoor battery for a long time. The use of a polyester film requires less reduction in mechanical properties (moisture resistance) when placed under high temperature and humidity for a long period of time. Moreover, the solar cell system is placed under direct sunlight. Therefore, the polyester film for solar battery back sheets is required to have less mechanical properties (weather resistance) when exposed to ultraviolet light for a long period of time. Further, the polyester film for solar battery back sheets is also required to electrically insulate the power generating element from the outside atmosphere (electrical insulation). In order to solve the above problems, various studies have been conducted so far (Patent Documents 1 to 4).

[Previous Technical Literature] [Patent Literature]

Patent Document 1: Japanese Patent Laid-Open Publication No. 2013-51395

Patent Document 2: Japanese Patent Laid-Open No. 2011-142128

Patent Document 3: International Publication No. 2012/8488

Patent Document 4: Japanese Patent Laid-Open Publication No. 2012-204797

The methods of Patent Documents 1 to 4 can obtain a polyester film which is excellent in moist heat resistance, weather resistance, and electrical insulation properties. However, since the solar cell is placed outdoors, the surface of the solar cell backsheet is exposed to various conditions such as wind, rain, dust, dust, and dead leaves. If it is exposed to wind, rain, dust, dust, dead leaves, etc. for a long time, the surface of the polyester film used in the solar cell back sheet is gradually worn away, and the film thickness is reduced (reducing film generation). The polyester film obtained by the methods of the above Patent Documents 1 to 4 is excellent in moist heat resistance, weather resistance, and electrical insulation. However, if it is used outdoors for a long period of time, film formation is reduced, and moist heat resistance and weather resistance are obtained. The problem of greatly reducing electrical insulation.

Therefore, an object of the present invention is to provide a polyester film which has a small reduction in the thickness of a film even if it is used outdoors for a long period of time (hereinafter, this property is sometimes referred to as film resistance reduction), and even When used outdoors for a long period of time, there is little reduction in moisture heat resistance, weather resistance, and electrical insulation properties (hereinafter, this property is sometimes referred to as durability).

In order to solve this problem, the present invention employs the following means. That is, (a) a polyester film for a solar cell back sheet having a polyester layer satisfying the following (1) to (3) in at least one surface layer (this layer is referred to as a P1 layer), and after the durability test The elongation retention rate is 40% or more.

(1) The thickness of the P1 layer is 30 μm or more and 250 μm or less.

(2) The surface roughness (Ra) of the P1 layer is more than 0.10 μm and is 0.50 μm or less.

(3) The amount of decrease in the thickness of the P1 layer after the durability test was 15 μm or less.

<Endurance test>

(i) The surface of the P1 layer side of the polyester film was irradiated with a illuminance of 180 W/m ² for 102 minutes under the conditions of a temperature of 65 ° C and a relative humidity of 50% RH using a xenon lamp (Suga Test Instruments, SC750). T-1).

(ii) After continuing the irradiation of the xenon lamp after (i), water of 16 ° C ± 5 ° C was sprayed on the P1 layer for 18 minutes (t-2) in an amount of 2.1 L ± 0.1 mL / min.

Furthermore, (t-1) + (t-2) = 120 minutes.

(iii) Repeat 1500 times (i) (ii).

(b) The polyester film for a solar cell back sheet according to (a), which comprises at least two layers of a polyester film.

(c) A polyester film for a solar cell back sheet according to (a) or (b), wherein durability test The partial discharge voltage maintenance rate after the test was 90% or more.

(d) The polyester film for a solar cell back sheet according to any one of (a) to (c), wherein the polyester resin composition constituting the P1 layer contains rutile-type titanium oxide and rutile-type titanium oxide. It is 14 to 20% by weight based on the entire polyester resin composition constituting the P1 layer.

(e) The polyester film for a solar cell back sheet according to any one of (a) to (d), wherein the polyester resin composition constituting the P1 layer contains -1,4-cyclohexane terephthalate The methyl ester unit (hereinafter referred to as CHT unit) is a polyester resin composition having a main constituent component, and the content of the polyester resin composition containing the CHT unit as a main constituent component is relative to the entire polyester resin composition constituting the P1 layer. , 14 to 20% by weight.

(f) The polyester film for solar cell back sheets according to any one of (a) to (e), wherein the polyester resin constituting the polyester film has an intrinsic viscosity of 0.6 to 1.0 dl/g, and the amount of terminal carboxyl groups is 5~20 equivalents/ton.

(g) The method for producing a polyester film for a solar cell back sheet according to any one of (a) to (f), which satisfies the following (4) to (6).

(4) A step of melt-kneading the polyester resin composition constituting the P1 layer by an extruder, extruding it, and cooling and solidifying it on a cooling cylinder to obtain an unaligned polyester film.

(5) The temperature of the cooling cylinder is Tg-70 ° C or more and Tg -30 ° C or less of the polyester resin constituting the P1 layer.

(6) The time (staying time) in contact with the cooling cylinder is 20 seconds or more and 120 seconds or less.

(h) The method for producing a polyester film for a solar cell back sheet according to any one of (a) to (f), which satisfies the following (4), (7) to (10).

(4) comprising the steps of: using a polyester resin composition constituting the P1 layer by using an extruder After melt-kneading, it is extruded, and solidified on a cooling cylinder to obtain an unaligned polyester film.

(7) A step of obtaining a uniaxially oriented polyester film by extending the unaligned polyester film obtained by (4) at an elongation temperature of 70 to 120 ° C and a stretching ratio of 2.0 to 4.0 times in the longitudinal direction.

(8) comprising the steps of: stretching the uniaxially oriented polyester film obtained by the step (7) in the width direction by an extension temperature of 70 to 150 ° C and a stretching ratio of 3.0 to 4.0 times to obtain a biaxial alignment polyester film. .

(9) A step of subjecting the biaxially oriented polyester film obtained by the step (8) to heat treatment at 205 to 240 ° C while relaxing in the width direction by 0 to 10%.

(10) The extension in the above (7) is carried out by using a stretching roll and a stretching nip roll, and the surface roughness Ra of the stretching roll is 0.5 to 1.5 μm, and the stretching roller and the stretching nip roll are sandwiched between The nip pressure is 0.4 to 1.0 MPa.

(i) The method for producing a polyester film for a solar cell back sheet according to any one of (a) to (f), which satisfies the following (4) to (10).

(4) A step of melt-kneading the polyester resin composition constituting the P1 layer by an extruder, extruding it, and cooling and solidifying it on a cooling cylinder to obtain an unaligned polyester film.

(5) The temperature of the cooling cylinder is Tg-70 ° C or more and Tg -30 ° C or less of the polyester resin constituting the P1 layer.

(6) The time (staying time) in contact with the cooling cylinder is 20 seconds or more and 120 seconds or less.

(7) A step of obtaining a uniaxially oriented polyester film by extending the unaligned polyester film obtained by (4) at an elongation temperature of 70 to 120 ° C and a stretching ratio of 2.0 to 4.0 times in the longitudinal direction.

(8) comprising the steps of: uniaxially aligning the polyester film obtained by the step (7) In the width direction, the stretching temperature is 70 to 150 ° C and the stretching ratio is 3.0 to 4.0 times to obtain a biaxially oriented polyester film.

(9) A step of subjecting the biaxially oriented polyester film obtained by the step (8) to heat treatment at 205 to 240 ° C while relaxing in the width direction by 0 to 10%.

(10) The extension in the above (7) is carried out by using a stretching roll and a stretching nip roll, the surface roughness Ra of the stretching roll is 0.5 to 1.5 μm, and the nip between the stretching roll and the extending nip roll is 0.4 to 1.0. MPa.

(j) A solar battery back sheet using the polyester film for a solar battery back sheet according to any one of (a) to (f).

(k) A solar cell using the solar battery back sheet as described in (j).

According to the present invention, it is possible to provide a polyester film for a solar cell back sheet which is excellent in film reduction resistance and durability. The polyester film for a solar cell back sheet of the present invention has excellent film resistance and durability, and thus the solar cell including the solar cell back sheet of the polyester film for a solar cell back sheet of the present invention can maintain its performance for a long period of time. , can extend the number of years of durability.

1‧‧‧ Backboard

2‧‧‧ Sealing material

3‧‧‧Power generation components

4‧‧‧Transparent substrate

5‧‧‧ Surface of the sealing material of the solar battery back sheet 2

6‧‧‧ Surface of the solar battery back plate opposite to the sealing material 2

Fig. 1 is a cross-sectional view schematically showing an example of a configuration of a solar cell using the solar cell back surface protective sheet of the present invention.

The polyester film of the present invention has a P1 layer in at least one skin layer. The phrase "having a P1 layer in at least one surface layer" means a single-layer polyester film containing only the P1 layer, and may be, for example, a P1 layer/P2 layer or a P1 layer/P2 layer/P1 layer or a P1 layer/P2 layer/P3. Layer layer Polyester film.

The thickness of the P1 layer of the present invention must be 30 μm or more and 250 μm. under. When the thickness of the P1 layer is less than 30 μm, the P1 layer of the present invention excellent in film reduction resistance cannot be used under conditions of ultraviolet irradiation and exposure to wind, rain, dust, dust, dead leaves, and the like for a long period of time. Fully maintain mechanical properties. In addition, when the thickness of the P1 layer is less than 30 μm, electrical insulation is insufficient, and insulation breakdown occurs when used under high voltage, and the polyester film for solar battery back sheets is not preferable. On the other hand, when the thickness of the P1 layer is thicker than 250 μm, the workability is inferior, and it is difficult to make the surface of the P1 layer a film surface having excellent film resistance and durability. Moreover, when the polyester film of the present invention is used as a polyester film for a solar cell back sheet, the overall thickness of the solar cell may become too thick and may be defective.

The surface roughness (Ra) of the P1 layer of the present invention must be greater than 0.10 μm and 0.50 μm or less. By setting the surface roughness of the P1 layer to the above range, the film reduction property can be improved. The mechanism for obtaining this effect is not limited to any theory, and the inventors and the like make the following assumptions.

By setting the surface roughness (Ra) of the P1 layer to the above range, When the surface of the film is wetted by water, the water non-wetting property becomes good. Therefore, even after the polyester film is exposed to wind and rain, the time during which water exists on the surface of the film can be shortened, and deterioration of the surface of the film due to hydrolysis can be suppressed. Further, by setting the surface roughness (Ra) of the P1 layer to the above range, ultraviolet rays can be reflected on the surface of the film. As a result, it is considered that the ultraviolet rays intruding into the inside of the film can be reduced, and deterioration of the resin constituting the film can be suppressed. Further, the film reduction resistance of the film can be classified into two stages of film resistance reduction in the initial stage and film reduction in the medium and long term. By setting the surface roughness of the P1 layer to the above range, the film-reducing property at the initial stage can be remarkably improved.

If the surface roughness (Ra) of the P1 layer is 0.10 μm or less, it cannot be suppressed. Since the resin constituting the film is deteriorated by the reflection of the ultraviolet ray, the film reduction speed of the film due to wind and rain or dust is increased. Further, when the surface roughness (Ra) of the P1 layer is more than 0.50 μm, the water on the surface of the film which is wetted by water is not wet, so that deterioration of the surface of the film cannot be suppressed, and the film reduction speed is increased. The surface roughness (Ra) of the P1 layer is more preferably 0.20 μm or more and 0.40 μm or less. The polyester film having the surface roughness (Ra) of the P1 layer in the above range can be obtained by the following production method or the kind and amount of the resin.

Even the surface roughness (Ra) of the P1 layer is thinner than the above range If the film is used outdoors for a long time, it is a little, but the film is also reduced. Since the film reduction progresses from the surface of the film, the surface roughness of the film changes with the passage of time. Therefore, even if the film having a surface roughness (Ra) of the P1 layer is in the above range, if the film is used outdoors for a long period of time, the surface roughness changes, and thus the high film reduction property cannot be maintained. The film-reducing property in the middle and long-term stages can be improved by the following resin or additive contained in the polyester resin composition constituting the film.

In the P1 layer of the present invention, the thickness of the P1 layer after the durability test described below must be reduced by 15 μm or less.

<Endurance test>

(i) The surface of the P1 layer side of the polyester film was irradiated with a illuminance of 180 W/m ² for 102 minutes under the conditions of a temperature of 65 ° C and a relative humidity of 50% RH using a xenon lamp (Suga Test Instruments, SC750). T-1).

(ii) After (i), while continuing to irradiate the xenon lamp, water of 16 ° C ± 5 ° C was sprayed on the P1 layer for 18 minutes (t-2) in an amount of 2.1 L ± 0.1 mL / min.

Furthermore, (t-1) + (t-2) = 120 minutes.

(iii) Repeat 1500 times (i) (ii).

The durability test is an accelerated test that assumes the use of a solar cell that is used for a long time outside exposure to wind, dust, dust, dust, dead leaves, and the like. In the durability test, the polyester film is gradually deteriorated by irradiation with ultraviolet rays of a xenon lamp or under high temperature and high humidity conditions. Further, since the deteriorated polyester film flows out by water spray, a decrease in film thickness (film reduction) occurs. Even in the polyester film which is excellent in moisture resistance, weather resistance, and electrical insulation, if the film is largely reduced, the performance is deteriorated during long-term use outdoors. When the reduction in the film thickness of the P1 layer due to the durability test exceeds 15 μm, the heat and humidity resistance, weather resistance, and electrical insulation properties are greatly reduced during long-term use outdoors, and the surface of the film is deteriorated. The polyester is covered, so the appearance is deteriorated. Further, since the thickness of the surface of the film due to the deterioration of the surface of the film is uneven or cracked, the water further erodes the inside of the film to accelerate the hydrolysis, so that the film properties are accelerated to be accelerated. It is preferable that the film thickness of the P1 layer is more preferably 12 μm or less. In a preferred embodiment, the amount of reduction in film thickness is small, but it is difficult to be less than 0.1 μm, and particularly preferably 0.1 μm or more and 10 μm or less.

The elongation retention of the polyester film of the present invention after the durability test must be 40% or more. If the elongation retention after the durability test is less than 40%, it is caused by cracking on the surface of the film, and water is accumulated in the crack generated on the surface of the film to promote hydrolysis, thereby causing a fatal effect on the film properties thereafter. The elongation retention after the durability test is more preferably 60% or more.

The polyester film of the present invention preferably has a partial discharge voltage maintenance ratio of 90% or more after the durability test. The partial discharge voltage maintenance rate was obtained by the following equation.

Partial discharge voltage maintenance rate (%) = (partial discharge voltage after durability test) (V)) / (partial discharge voltage (V) before durability test) × 100

When the partial discharge voltage maintenance rate is 90% or more, the electrical insulation property can be maintained even if it is placed outdoors for a long period of time. Therefore, it is preferable as an insulating material used in an environment exposed to the outside for a long period of time. More preferably 95% or more. Further, the polyester film of the present invention preferably has a partial discharge voltage (i.e., a partial discharge voltage before the weather resistance test) of 1000 V or more.

The P1 layer of the present invention contains a polyester resin as a main constituent component. Here, the term "polyester resin as a main component" means that the polyester resin contains more than 50% by mass based on the resin constituting the P1 layer. Specific examples of the polyester resin constituting the P1 layer include polyethylene terephthalate, polyethylene-2,6-naphthalenedicarboxylate, polytrimethylene terephthalate, and poly(terephthalic acid). Butadiene ester, polylactic acid, and the like. Further, the polyester resin used in the present invention can be obtained by a condensation condensation of 1) a dicarboxylic acid or an ester-forming derivative thereof (hereinafter collectively referred to as "dicarboxylic acid component") with a diol component, and 2) in one molecule. It is obtained by polycondensation of a compound having a carboxylic acid or a carboxylic acid derivative and a hydroxyl group, and a combination of 1) and 2). Further, the polymerization of the polyester resin can be carried out according to the usual practice.

In 1), examples of the dicarboxylic acid component include malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecanedioic acid, and dimer acid. , an aliphatic dicarboxylic acid such as eicosanedioic acid, pimelic acid, sebacic acid, methylmalonic acid or ethylmalonic acid; adamantane dicarboxylic acid An alicyclic dicarboxylic acid such as an enedicarboxylic acid, a cyclohexanedicarboxylic acid or a decahydronaphthalene dicarboxylic acid; terephthalic acid, isophthalic acid, citric acid, 1,4-naphthalenedicarboxylic acid, 1, 5-naphthalene dicarboxylic acid, 2,6-naphthalene dicarboxylic acid, 1,8-naphthalene dicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-diphenyl ether dicarboxylic acid, 4 , 4'-diphenylstilbene dicarboxylic acid, sodium isophthalate-5-sulfonate, ethylbenzene dicarboxylic acid, stilbene dicarboxylic acid, phenanthrene dicarboxylic acid, 9,9'-bis(4-carboxybenzene An aromatic dicarboxylic acid such as citric acid; or an ester derivative thereof or the like. Further, these may be used alone or in combination.

Further, at least one carboxyl terminal of the above dicarboxylic acid component may be used. An oxo-acid compound obtained by condensing an oxo acid such as lactide, d-lactide or hydroxybenzoic acid or a derivative thereof or a plurality of oxyacids.

Next, as a diol component, a representative example is ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-butanediol, 1,3-butanediol and other aliphatic diols; cyclohexanedimethanol, spirodiol An alicyclic diol such as isosorbide; an aromatic diol such as bisphenol A, 1,3-benzenedimethanol, 1,4-benzenedimethanol or 9,9'-bis(4-hydroxyphenyl)fluorene . Further, these may be used alone or in combination as needed. Further, a dihydroxy compound formed by condensing at least one hydroxyl group terminal of the above diol component with a glycol may also be used.

In 2), as a carboxylic acid or a carboxylic acid derivative and a hydroxy group in one molecule Examples of the compound of the group include oxyacids and derivatives thereof such as 1-lactide, d-lactide and hydroxybenzoic acid, oligomers of oxyacids, and carboxyl groups of one of the dicarboxylic acids. Oxyacid condensation.

The dicarboxylic acid component and the diol component constituting the polyester resin may be selected from one of the above, and may be copolymerized, or may be selected from several kinds to be copolymerized.

Further, the polyester resin constituting the P1 layer may be a single type or a mixture of two or more kinds of polyester resins. From the viewpoint of mechanical strength and workability, it is preferred to use polyethylene terephthalate (PET) as a main component.

The resin constituting the P1 layer of the present invention contains a polyester resin as a main component as described above, and when the intrinsic viscosity is 0.60 dl/g or more and 1.00 dl/g or less, and the terminal carboxyl group amount is 20 equivalent/ton or less, the resin is resistant. It is preferable because it has good moist heat, moldability, and durability. If the intrinsic viscosity is 0.65 dl/g or more and 0.80 dl/g or less, it is resistant. It is preferred because it has better wet heat, film formability, and durability. When the intrinsic viscosity IV satisfies the above range and the amount of terminal carboxyl groups is 20 equivalents/ton or less, the moist heat resistance is further improved, which is preferable. In this way, the resin constituting the P1 layer is a solar cell backsheet polyester which is excellent in durability, moist heat resistance, and moldability, and has a specific viscosity and a terminal carboxyl group content in a range of the above-mentioned range. film.

The polyester film for solar battery back sheet of the present invention constitutes a P1 layer The number average molecular weight of the polyester resin is preferably from 8,000 to 40,000, more preferably from 9000 to 30,000, more preferably from 10,000 to 20,000. The number average molecular weight of the polyester resin constituting the P1 layer mentioned herein means that the P1 layer is separated from the polyester film for solar cell back sheet of the present invention and dissolved in hexafluoroisopropanol (HEIP), according to The gel was measured by gel permeation chromatography (GPC method) and detected by a differential refractometer, and polyethylene terephthalate (PET-5R: Mw 55800) having a known molecular weight and dimethyl terephthalate were used. The value obtained as a standard sample. When the number average molecular weight of the polyester resin constituting the P1 layer is less than 8,000, there is a possibility that the long-term durability of the sheet such as moist heat resistance or heat resistance is lowered, which is not preferable. Moreover, when it exceeds 40,000, it is difficult to polymerize or it is difficult to form a film by extrusion of a resin by an extruder, even if it is polymerizable. Further, in the polyester film for a solar battery back sheet of the present invention, it is preferred that the P1 layer is aligned in a single axis or a double axis. When the P1 layer is aligned in a uniaxial or biaxial manner, characteristics such as moist heat resistance or heat resistance can be improved by alignment crystallization.

The polyester resin composition constituting the P1 layer of the present invention contains titanium oxide particles The content of the polyester resin composition constituting the P1 layer is preferably 14% by mass or more and 20% by mass or less. As a result, the ultraviolet absorbing energy generated by the titanium oxide particles and the light reflectivity can be activated, and the effect of reducing the ultraviolet ray irradiation for a long period of time can be obtained, so that the resistance in the initial stage and the medium and long term can be improved. membrane Reduced sex. When the surface roughness of the P1 layer is 0.20 μm to 0.40 μm, a large film-reducing effect at the initial stage can be obtained. The mechanism from which the effect comes from is not clear, but it is presumed that if a certain amount of titanium oxide is contained so that the surface roughness of the P1 layer is within a specific range, the ultraviolet ray is effectively reflected on the surface of the P1 layer, so that the ultraviolet ray does not reach the polyester film. Internal, it can suppress the deterioration of polyester. In addition, when the titanium oxide particles are contained in the above range in the polyester resin composition constituting the P1 layer of the present invention, the power generation efficiency of the solar cell on which the thin film of the present invention is mounted can be improved. When the content of the titanium oxide particles is less than 14% by mass, the above effects may not be sufficiently obtained. If it is more than 20% by mass, the film formability may be deteriorated. Further, when it is coextruded with other layers and laminated, the adhesion may be deteriorated. Further, in view of the fact that titanium oxide has excellent ultraviolet resistance and light reflectivity, it is more preferable to use rutile-type titanium oxide.

Here, the above-mentioned particles are contained in the polyester resin constituting the P1 layer. In the method, it is preferred to use a method in which a polyester resin and a particle are melt-kneaded using a vented biaxial kneading extruder or a tandem extruder. Here, when the polyester resin contains particles, if the polyester resin is subjected to a heat load, the polyester resin is extremely deteriorated. Therefore, from the viewpoint of heat and humidity resistance, it is preferred to prepare a high-concentration main particle having a particle content larger than the amount of the particles of the polyester resin constituting the P1 layer, and mixing and diluting it with the polyester resin to produce Become the P1 layer of the desired particle content.

In the P1 layer of the present invention, in addition to the above titanium oxide particles or carbon particles Further, a heat-resistant stabilizer, an oxidation-resistant stabilizer, an ultraviolet absorber, a UV stabilizer, an organic/inorganic lubricant, or an organic/inorganic fine particle may be blended as needed within a range not impairing the effects of the present invention. Additives such as fillers, nucleating agents, dyes, dispersants, coupling agents, or bubbles. For example, when a UV absorber is selected as an additive, the ultraviolet resistance of the film of the present invention can be further improved. Also, you can add A new pattern is imparted by adding an antistatic agent or the like to enhance electrical insulation or to contain organic/inorganic fine particles or bubbles to exhibit light reflectivity or to add a color to be colored.

The polyester resin composition constituting the P1 layer of the present invention contains p-benzoic acid The formic acid-1,4-cyclohexanedimethyl ester unit (hereinafter, also referred to as CHT unit) is a polyester resin having a main constituent component, and the content thereof is preferably 14% by mass based on the entire polyester resin composition constituting the P1 layer. % or more and 20% by mass or less. Thereby, it is possible to impart heat and humidity resistance, and it is possible to obtain an effect of improving film resistance in the initial stage and the medium and long term stage. When the surface roughness of the P1 layer is 0.20 μm to 0.40 μm, a large film-reducing effect at the initial stage can be obtained. The mechanism from which the effect is derived is not clear, but it is presumed that the resin constituting the polyester film contains a resin having a CHT unit as a constituent component having a large viscosity characteristic, and the polyester which is deteriorated by ultraviolet rays is discharged to the system. Speed outside. If the content of the CHT unit is less than 14% by mass, the above effects may not be sufficiently obtained. If it is more than 20% by mass, the film formability may be deteriorated. Furthermore, in the present invention, the content of the polyester resin having the CHT unit as a main constituent component as a whole of the polyester resin composition constituting the polyester film is set as the polyester resin composition constituting the polyester film. The total amount added.

If the heat accumulation and durability are improved, the composition of the P1 layer is increased. When the polyester film of the P1 layer single film is formed into a film, the intrinsic viscosity of the ester resin may deteriorate in film formability and workability. Therefore, the polyester film of the present invention is preferably a laminated polyester film comprising at least two layers of a substrate layer (P2 layer) other than the P1 layer. Further, when two or more layers of the polyester film of the present invention are used for a solar cell back sheet, the P1 layer is placed on the surface layer of the solar cell back sheet (exposed to the side of the wind and rain). In the present invention, it is preferred to coextrude the P2 layer and the P1 layer as a polyester for solar battery back sheets. film. When it is manufactured by a sticking method, it will be curled at the time of bonding, or it will advance deterioration by the adhesive used for bonding.

The P2 layer and the P1 layer are mainly composed of a polyester resin composition. ingredient. As long as it has the same composition as the P1 layer, it can be simultaneously formed into a film (co-extrusion) with the P1 layer, and the adhesion to the P1 layer is also good.

The inherent viscosity of the polyester resin constituting the P2 layer of the present invention is 0.50 When the amount of the terminal carboxyl group is 5 equivalents/ton or more and 40 equivalents/ton or less, the film forming property and the processability are good, and dl/g or more and 0.80 dl/g or less are preferable. When the intrinsic viscosity is 0.55 dl/g or more and 0.75 dl/g or less, and the terminal carboxyl group content is 10 equivalent/ton or more and 35 equivalent/ton or less, the moist heat resistance can be further improved, which is preferable.

Further, the composition of the polyester resin constituting the P2 layer is contained in the titanium oxide particles. When the amount is 14% by mass or less based on the entire amount of the polyester resin composition constituting the P2 layer, film formability and workability are good, which is preferable. More preferably, it is 1 mass% or more and 14 mass% or less.

Further, the polyester resin composition constituting the P2 layer is preferably contained The CHT unit is a polyester resin having a main constituent component of 1% by mass or more and 20% by weight or less. By using the polyester resin composition constituting the P2 layer as the above resin, it is preferable to make the adhesion to the P1 layer good at the time of film formation.

In addition, when the thickness of the P2 layer is 30 μm or more and 250 μm or less, film formability and workability are good, which is preferable.

The polyester film of the present invention preferably has a total film thickness of 50 μm or more and 1000 μm or less. When the total thickness of the film is 250 μm or more, the partial discharge voltage is high (electrical insulation properties are good), which is preferable. More preferably, it is 300 μm or more, and further preferably 350 μm or more. On the other hand, if it exceeds 500 μm, it has film forming properties. Poor processability.

The polyester film for solar cell back sheet of the present invention is as described above and durable Excellent in properties and film resistance. Therefore, the solar cell equipped with the polyester film for a solar cell back sheet of the present invention can be a solar cell which does not have a reduced output even if it is placed outdoors for a long period of time.

The polyester film for a solar cell back sheet of the present invention can be, for example, by the following Obtained by the manufacturing methods described in (a), (b), and (c).

(a) A method for producing a polyester film for a solar cell back sheet, which satisfies The following (4) ~ (6).

(4) A step of melt-kneading the polyester resin composition constituting the P1 layer by an extruder, extruding it, and cooling and solidifying it on a cooling cylinder to obtain an unaligned polyester film.

(5) The temperature of the cooling cylinder is Tg-70 ° C or more to Tg -30 ° C of the polyester resin constituting the P1 layer.

(6) The time (staying time) in contact with the cooling cylinder is 20 seconds or more and 120 seconds or less.

(b) A method for producing a polyester film for a solar cell back sheet, which satisfies The following (4), (7) ~ (10).

(4) A step of melt-kneading the polyester resin composition constituting the P1 layer by an extruder, extruding it, and cooling and solidifying it on a cooling cylinder to obtain an unaligned polyester film.

(7) A step of obtaining a uniaxially oriented polyester film by extending the unaligned polyester film obtained in (4) at an elongation temperature of 70 to 120 ° C and a stretching ratio of 2.0 to 4.0 times in the longitudinal direction.

(8) comprising the steps of: extending the uniaxially oriented polyester film obtained by the step (7) in the width direction by an extension temperature of 70 to 150 ° C and a stretching ratio of 3.0 to 4.0 times. Stretching to obtain a biaxially oriented polyester film.

(9) A step of subjecting the biaxially oriented polyester film obtained by the step (8) to heat treatment at 205 to 240 ° C while relaxing in the width direction by 0 to 10%.

(10) The extension in the above (7) is carried out by using a stretching roll and a stretching nip roll, wherein the surface roughness Ra of the stretching roll is 0.5 to 1.5 μm, and the pinch between the stretching roll and the extending nip roll is 0.4~ 1.0 MPa.

(c) A method for producing a polyester film for a solar cell back sheet, which satisfies The following (4) ~ (10).

(4) A step of melt-kneading the polyester resin composition constituting the P1 layer by an extruder, extruding it, and cooling and solidifying it on a cooling cylinder to obtain an unaligned polyester film.

(5) The temperature of the cooling cylinder is Tg-70 ° C or more and Tg -30 ° C or less of the polyester resin constituting the P1 layer.

(6) The time (staying time) in contact with the cooling cylinder is 20 seconds or more and 120 seconds or less.

(7) A step of obtaining a uniaxially oriented polyester film by extending the unaligned polyester film obtained in (4) at an elongation temperature of 70 to 120 ° C and a stretching ratio of 2.0 to 4.0 times in the longitudinal direction.

(8) comprising the steps of: stretching the uniaxially oriented polyester film obtained by the step (7) in the width direction by an extension temperature of 70 to 150 ° C and a stretching ratio of 3.0 to 4.0 times to obtain a biaxial alignment polyester film. .

(9) A step of subjecting the biaxially oriented polyester film obtained by the step (8) to heat treatment at 205 to 240 ° C while relaxing in the width direction by 0 to 10%.

(10) The extension in the above (7) is carried out by using a stretching roll and a stretching nip roll, and the surface roughness Ra of the stretching roll is 0.5 to 1.5 μm, and the stretching roller and the stretching nip roller are sandwiched. The pressure is 0.4~1.0MPa.

First, the method of (a) will be described.

The polyester film of the present invention preferably comprises the steps of: melt-kneading the polyester resin composition constituting the P1 layer by an extruder, extruding it, and cooling and solidifying on a cooling cylinder to obtain an unaligned polyester film. In the case where the polyester film of the present invention is a laminated polyester film containing a P2 layer other than the P1 layer, it is preferred to include a step of heating and melting the raw materials of each of the P1 layer and the P2 layer in two extruders. The film is extruded from the nozzle onto the cooled casting cylinder to obtain an unaligned laminated polyester film (melt casting method, co-extrusion method).

The temperature of the cooling cylinder is preferably a glass transition temperature (hereinafter referred to as Tg) of the polyester resin constituting the P1 layer of -70 ° C or more and Tg -30 ° C or less. By setting the temperature of the cooling cylinder to the above range, the thermal crystallization degree of the polyester resin constituting the unaligned polyester film can be extended to the longitudinal direction while maintaining the appropriate degree of thermal crystallization, and the surface of the P1 layer can be easily made. The thickness is more than 0.1 μm and is 0.5 μm or less. When the temperature of the cooling cylinder is set to be lower than the Tg-70 ° C of the polyester resin constituting the P1 layer, the cooling of the polymer is rapid, the thermal crystallization is greatly generated, and the variation of the thermal crystallization becomes conspicuous, so that it is difficult. The surface roughness of the film is set to be in the range of 0.1 to 0.5 μm or extended in the longitudinal direction to cause cracking of the film. The temperature of the cooling cylinder is preferably Tg-60 ° C or more and Tg-35 ° C or less of the polyester resin constituting the P1 layer, and more preferably Tg-55 ° C or more and Tg - 40 ° C or less.

Moreover, the time (residence time) in contact with the above-mentioned cooling cylinder is preferably 20 seconds or more and 120 seconds or less. By setting the time of contact with the cooling cylinder to the above range, the discharged polymer can be sufficiently cooled, and the longitudinal direction can be extended while reducing the variation in the thermal crystallization degree in the polyester film, and the P1 layer can be reduced. The surface roughness is deviated, and the surface roughness of the P1 layer can be easily made larger than 0.10 μm and 0.50 μm or less. versus The contact time (residence time) of the cooling cylinder is preferably 20 seconds or more and 60 seconds or less, and more preferably 25 seconds or more and 45 seconds or less. When the temperature is less than 20 seconds, the cooling of the polymer is rapid, the thermal crystallization is greatly generated, and the variation of the thermal crystallization becomes remarkable. Therefore, it is difficult to set the surface roughness of the film to a range of 0.1 to 0.5 μm or The film is broken after extending in the length direction.

Thereafter, the polyester film of the present invention can be obtained by subjecting the above unstretched polyester film to a previously known stretching and heat treatment.

Next, the method of (b) will be described.

In the polyester film of the present invention, the polyester resin composition constituting the P1 layer is melt-kneaded by an extruder, extruded, and cooled and solidified on a cooling cylinder to obtain an unaligned polyester film, which is satisfied by the following (7) Obtained in the elongation step of the step (10) and the manufacturing method of the heat treatment step.

(7) comprising the steps of: stretching the unaligned polyester film in the longitudinal direction at an elongation temperature of 70 to 120 ° C and a stretching ratio of 2.0 to 4.0 times to obtain a uniaxially oriented polyester film.

(8) comprising the steps of: stretching the uniaxially oriented polyester film obtained by the step (7) in the width direction, extending at a temperature of 70 to 150 ° C, and an extension ratio of 3.0 to 4.0 times, thereby obtaining a biaxial alignment polyester. film.

(9) A step of subjecting the biaxially oriented polyester film obtained by the step (8) to heat treatment at 205 to 240 ° C while relaxing in the width direction by 0 to 10%.

(10) The extension in the above (7) is carried out by using a stretching roll and a stretching nip roll, wherein the surface roughness Ra of the stretching roll is 0.5 to 1.5 μm, and the pinch between the stretching roll and the extending nip roll is 0.4~ 1.0 MPa.

Extension in the length direction is carried out using a stretching roll and a stretching nip roll Preferably, the heating in the stretching step is carried out by means of a heated stretching roll. In addition, when the surface roughness Ra of the stretching roll is 0.5 to 1.5 μm, and the nip between the stretching roll and the stretching nip roll is 0.4 to 1.0 MPa, generation of film breakage or the like can be suppressed, and productivity is good, and The surface roughness of the P1 layer is easily made larger than 0.10 μm and 0.50 μm or less. In particular, if the surface roughness Ra of the stretching rolls is 0.7 to 1.2 μm, and the nip between the stretching rolls and the stretching nip rolls is 0.5 to 0.8 MPa, the productivity can be maintained well, and at the same time, the obtained one can be obtained. The polyester film is preferred because it has good durability and film reduction resistance.

The extension in the width direction is preferably a film obtained by the step (7) The surface of the film is gripped by the clamp to the tenter, and is extended by 3 to 4 times in a direction perpendicular to the longitudinal direction (width direction) in an environment heated to a temperature of 70 to 150 °C. By setting the stretching temperature and the stretching ratio in the longitudinal direction and the width direction to the above range, it is possible to suppress the occurrence of film breakage and the like, and to improve the productivity, and the surface roughness of the P1 layer can be made larger than 0.1 μm and 0.50 μm. the following. In addition, when the area magnification obtained by multiplying the stretching ratio in the longitudinal direction and the width direction is 9 to 15 times, the productivity can be maintained well, and the durability and film resistance of the obtained polyester film can be reduced. Good sex, so it is better. Further, if the step of cooling the roll group at a temperature of 20 to 50 ° C is included between the steps (7) and (8), productivity can be improved, which is preferable.

If included, the side of the biaxial alignment polyester film to be obtained by the step (8) When the heat treatment is performed at 205 to 240 ° C and the film is relaxed by 0 to 10% in the width direction, the surface shape formed by the P1 layer can be easily maintained as it is.

Next, the method of (c) will be described.

The method (c) is a method in which an unstretched polyester film is obtained by the method satisfying (a), and the film is stretched and heat-treated by the method of (b). The production method satisfying (c) is preferable because the polyester film of the present invention can be obtained stably and with good productivity.

Since the polyester film of the present invention is excellent in film reduction resistance and durability, it can be preferably used for solar battery back sheets. Further, in the case where the polyester film of the present invention is a laminated polyester film comprising a P1 layer or a P2 layer, it is preferable to use the P1 layer as the outermost layer of the solar cell back sheet (the symbol 6 side of Fig. 1). The form is used.

Further, the solar cell including the solar cell back sheet using the polyester film of the present invention can maintain its performance for a long period of time and can prolong the durability.

[Measurement method and evaluation method of characteristics] (1) Intrinsic viscosity

Dissolve the measurement sample (polyester resin (raw material) or polyester film) in 100 ml of o-chlorophenol (solution concentration C (measure sample weight / solution volume) = 1.2 g / 100 ml), using an Oswald viscometer (Ostwald) Viscometer) The viscosity of the solution at 25 ° C was measured. Further, the viscosity of the solvent was measured in the same manner. Using the obtained solution viscosity and solvent viscosity, [η] was calculated according to the following formula (I), and the obtained value was defined as the intrinsic viscosity (IV).

Ηsp/C=[η]+K[η] ² ‧C...(I)

(Here, ηsp = (solution viscosity / solvent viscosity) -1, and K is the Huggins constant (set to 0.343)).

In the case where an insoluble matter such as inorganic particles is present in the solution in which the measurement sample is dissolved, the measurement is carried out by the following method.

i) The measurement sample was dissolved in 100 mL of o-chlorophenol to prepare a solution having a solution concentration of 1.2 g/100 mL. Here, the weight of the measurement sample supplied to o-chlorophenol was used as the measurement sample weight.

Ii) Next, the solution containing the insoluble matter is filtered, and the weight of the insoluble matter is measured and the volume of the filtrate after the filtration is measured.

Iii) adding o-chlorophenol to the filtered filtrate so that (measured sample weight (g) - insoluble matter weight (g)) / (filtered filtrate volume (mL) + additional o-chlorophenol The volume (mL) was adjusted so as to be 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 is prepared, when the weight of the insoluble matter is 0.2 g when the solution is filtered, and the volume of the filtrate after filtration is 99 mL, the addition of o-chlorophenol is carried out. Adjustment of 51mL ((2.0g-0.2g) / (99mL + 51mL) = 1.2g / 100mL))

Iv) using the solution obtained in iii), measuring the viscosity at 25 ° C using an Oswald viscometer, using the obtained solution viscosity, solvent viscosity, and calculating [η] by the above formula (C), The value is taken as the intrinsic viscosity (IV).

(2) The amount of terminal carboxyl groups

The amount of terminal carboxyl groups was determined according to the method of Maulice and was determined according to the following method. (Document MJ Maulice, F. Huizinga, Anal. Chim. Acta, 22 363 (1960)) 2 g of a test sample (polyester resin (raw material) or polyester film) was dissolved in o-cresol/chloroform at a temperature of 80 ° C. In 50 mL (weight ratio 7/3), titration was carried out by a 0.05 N KOH/methanol solution, and the terminal carboxyl group concentration was measured to show the equivalent/polyester 1t value. Further, the titration indicator is phenol red, and the yellowing green color is changed to yellowish green as the end point of the titration. In the case where an insoluble matter such as inorganic particles is present 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 weight of the measurement sample is used as a value. The correction of the weight of the sample is determined.

(3) Thickness of P1 and P2 layers

Using a microtome, cutting perpendicular to the surface of the polyester film As a small piece, the cross section was enlarged to 1000 to 5000 times using a field emission scanning electron microscope JSM-6700F (manufactured by JEOL Ltd.) to observe and photograph. The thickness of the P1 layer and the P2 layer was obtained from the cross-sectional photograph by the magnification calculation. Further, the number of samples is n=10, and the average value thereof is set.

(4) Surface roughness (Ra)

The surface roughness (Ra) of the polyester film was measured under the following conditions using a high-precision fine shape measuring device of the stylus method in accordance with JIS-B0601 (1994).

Measuring device: three-dimensional micro shape measuring device (manufactured by Kosuke Research Institute Model ET-4000A)

Analytical equipment: 3D surface roughness analysis system (manufactured by Kosaka Research Institute Model No. TDA-31)

Stylus: front end radius 0.5μmR, diameter 2μm, manufactured by DIAMOND

Acupressure: 100μN

The measurement direction and the calculation method were measured 10 times in the film longitudinal direction and the film width direction. The average of the 20 measurements was taken as the surface roughness.

(5) Titanium oxide content

The amount of titanium element contained in the film was determined by the following method using an ICP emission spectrometer (manufactured by PerkinElmer Co., Ltd.: OPTIMA 4300 DV), and the titanium oxide content was converted based on the amount of the titanium element obtained. In the case where the polyester film is a laminated polyester film, the thickness of each layer of the film is confirmed by the method of (3), and the surface of the laminated polyester film is cut, and a sample is taken from each layer to determine the thickness of each layer. Titanium oxide content.

i) Weigh the sample taken in a platinum crucible, add sulfuric acid, use a hot plate and The burner is carbonized.

Ii) Further, the mixture was heated at 550 ° C for 2 hours in an electric furnace to carry out ashing treatment.

Iii) adding a mixed solvent of sodium carbonate-boric acid to the obtained ash, melting it by heating with a burner, and then dissolving it by adding dilute nitric acid and hydrogen peroxide after cooling, and using the obtained sample as a sample solution, introducing ICP emission analysis The titanium element is quantified in the device.

(6) Heat and humidity resistance

The polyester film was cut into a shape of a measuring piece of 10 mm × 200 mm, and then treated in a high-acceleration life test apparatus pressure cooker (ESPEC (manufactured)) at a temperature of 125 ° C and a relative humidity of 100% RH for 48 hours. Thereafter, the elongation at break was measured based on ASTM-D882 (1997). In addition, the measurement system was set to a collet pitch of 50 mm, a tensile speed of 300 mm/min, and a measurement count of n=5. Further, after measuring each of the longitudinal direction and the width direction of the sheet, the average value of the sheets was used as damp heat. Breaking elongation after the test. According to the elongation at break after the obtained damp heat test, the heat and humidity resistance was determined in the following manner.

The elongation at break after the damp heat test is more than 40% of the elongation at break before the damp heat test: A

The elongation at break after the damp heat test is 20% or more of the elongation at break before the damp heat test and less than 40%: B

The elongation at break after the damp heat test is 10% or more of the elongation at break before the damp heat test and less than 20%: C

The elongation at break after the damp heat test is less than 10% of the elongation at break before the damp heat test: D

The heat and humidity resistance system A~C is good, and A is the best.

(7) Partial discharge voltage

The electrical insulation was evaluated by measuring the partial discharge on the upper portion of the P1 layer based on the following measurement method.

Standard specification: IEC60664/A2:2002 4.1.2.4

Partial Discharge Testing Machine: manufactured by Kikusui Electronics Industry Co., Ltd., KPD2050

Maximum applied voltage: 1.6kV

Maximum applied voltage time: 5 seconds

Initial voltage charge threshold: 1.0pC

Quenching voltage charge threshold: 1.0pC

Test time: 22.0sec

Measurement pattern: trapezoid

(8) Characteristics after durability test

According to JIS K7350-2 (2008), the durability test was carried out under the following conditions. Thereafter, each characteristic was measured.

<Endurance test>

(i) The surface of the P1 layer side of the polyester film was irradiated with a illuminance of 180 W/m ² for 102 minutes under the conditions of a temperature of 65 ° C and a relative humidity of 50% RH using a xenon lamp (Suga Test Instruments, SC750). T-1).

Ii) After (i), while continuing to irradiate the xenon lamp, water of 16 ° C ± 5 ° C was sprayed on the P1 layer for 18 minutes (t-2) in an amount of 2.1 L ± 0.1 mL / min.

Furthermore, (t-1) + (t-2) = 120 minutes.

(iii) Repeat 1500 times (i) (ii).

(8-1) Reduction in thickness of the P1 layer after the durability test

After measuring the thickness of the P1 layer after the durability test by the method of (3), the thickness (μm) of the P1 layer before the durability test and the thickness (μm) of the P1 layer after the durability test were determined as the durability test. The amount of decrease in thickness of the subsequent P1 layer (μm).

(8-2) Durability retention after durability test

The elongation at break before and after the durability test was measured based on ASTM-D882 (1997). In addition, the measurement system was set to a crosshead pitch of 50 mm, a tensile speed of 300 mm/min, and a measurement count of n=5, and each of the longitudinal direction and the width direction of the sheet was measured, and the average value thereof was used as each. The elongation of the fracture. The elongation at break (%) after the durability test/the elongation at break (%) before the durability test × 100 was taken as the elongation retention ratio (%) after the durability test, and evaluated according to the following.

After the durability test, the elongation retention rate is 60% or more: A

After the durability test, the elongation retention rate is 40% or more and less than 60%: B

After the durability test, the elongation retention rate is 20% or more and less than 40%: C

Case where the elongation retention rate after the durability test is less than 20%: D

Evaluation of A~B is good.

(8-3) Partial discharge voltage maintenance rate after durability test

After the partial discharge voltage after the durability test was measured by the method of (7), the partial discharge voltage (V) after the durability test/partial discharge voltage (V) × 100 before the durability test was determined as the durability test. Partial discharge voltage maintenance rate (%).

(9) Glass transition temperature (Tg) of the polyester resin constituting the P1 layer

According to JIS K7121 (1999), the differential scanning calorimeter "Robot DSC-RDC220" manufactured by Seiko Instruments Inc. was used, and the Disk Session "SSC/5200" was used for data analysis, and the measurement was carried out by the following method.

The resin constituting the P1 layer was cut from the polyester film using a microtome for measurement of a sample. 5 mg of the measurement sample obtained by weighing was placed in a sample pot, and heated from 25 ° C to 300 ° C (1 s RUN) at a temperature increase rate of 20 ° C / min, and kept in this state for 5 minutes, and then became 25 ° C or less. The way is cold. Then, the temperature was measured again from 25 ° C to 300 ° C at a temperature increase rate of 20 ° C / min, and a 2 nd RUN differential scanning calorimeter measurement chart was obtained (the vertical axis was set as thermal energy and the horizontal axis was set as temperature). Regarding the 2nd RUN differential scanning calorimetry chart, in the stepwise change portion of the glass transition, the curve of the stepwise change of the straight line in the direction of the longitudinal axis and the step of the glass transition in the straight line of each reference line is extended. The glass transition temperature (Tg) (°C) was determined at the point of intersection. When a stepwise change of two or more glass transitions was observed, the glass transition temperature was determined, and the average value of the temperatures was defined as the glass transition temperature (Tg) (° C.) of the sample.

(10) Film forming properties

The film formation property was judged in the following manner in terms of the frequency of film breakage at the time of film formation.

Film rupture is 1 time / 1 day or more: A

Film rupture is 1 time / 12 hours or more and less than 1 day: B

Film rupture is 1 time / 5 hours or more and less than 12 hours: C

Film rupture is 1 time / less than 5 hours: D

The film-forming system A was good, and the BCD was inferior.

(11) Output maintenance characteristics of solar panel

Coating the surface of the film on the opposite side of the P1 layer of the polyester film (the film surface having a surface roughness (Ra) of more than 0.10 μm and 0.50 μm or less) to the polyester adhesive main agent LX703VL and the polyisocyanate hardener KR90 (both An adhesive (dry weight 4 g/m ² ) mixed with a weight ratio of 15:1 for the Dainippon Ink Chemical Industry Co., Ltd. Then, this was dry-laminated with an alumina transparent vapor-deposited film (Barrialox (registered trademark) manufactured by TORAY ADVANCED FILM (12 μm thick)) as a gas barrier film to prepare a back sheet for a solar cell. An ethylene-vinyl acetate copolymer resin sheet, a solar cell, and a translucent glass plate are laminated on the side of the solar cell back sheet laminated with the gas barrier film, and are heated and compressed by a lamination step, thereby integrating The solar cell module is formed. Further, a panel input step of taking out the solar cell module to the solar cell panel line is taken out, and in the primer application step, a primer is applied to the adhesion surface to the aluminum frame. Then, in the drying step, the drying time of the primer is left for about 1 minute, and then carried out to the frame side by the carry-out step. On the other hand, the assembled aluminum frame is put into the frame side of the frame. The aluminum frame has a tab for supporting the surface side of the solar cell module in which the solar cell is disposed, and is disposed on the surface side of the solar cell module, and has a structure that is disposed over the entire circumference of the end portion of the solar cell module. The shape is such that the light-receiving side of the solar cell module is in an open state. Then, the solar cell module to which the primer is applied is transferred, and the aluminum frame to which the primer is applied and the solar cell module (the solar cell panel adhesion step) are placed in the panel bonding step. Finally, the solar panel is fabricated by installing the molding strip as needed during the panel mounting step. The back side of the solar cell panel panel obtained by the above steps includes a solar cell backsheet, and the P1 layer is located at the outermost layer of the solar cell backsheet. It was confirmed that there was no crack or crack on the back surface of the fabricated solar cell panel, and the solar cell panel was treated at a temperature of 85 ° C and a relative humidity of 85% RH for 3,000 hours, and the appearance and output of the back surface were lowered (JIS-C8913 ( 1998)) Evaluation.

No cracks, cracks, no output reduction (output reduction is less than 10% relative to the initial output): A

Some cracks and cracks were observed, and some of the output was reduced (the output reduction was 10% or more and less than 30% relative to the initial output): B

Cracks and cracks were observed, and the output was greatly reduced (the amount of reduction in output was 30% or more and less than 50% relative to the initial output): C

Rupture, cracks are large, almost no output (output reduction is 50% or more and less than 80% relative to the initial output): D

Cracking, cracking, no output (output reduction compared to the initial output of 80% or more): E

A~C is good, of which A is the best.

[Examples]

Hereinafter, the present invention will be described by way of examples, but the present invention is not limited thereto.

(Polyester resin raw material) <PET material A>

100 parts by mass of terephthalic acid as a dicarboxylic acid component and 100 parts by mass of ethylene glycol as a diol component are used, and a polycondensation reaction is carried out using magnesium acetate, antimony trioxide or phosphorous acid as a catalyst. Then, the obtained polyethylene terephthalate was dried at 160 ° C for 6 hours to be crystallized, and then subjected to 220 ° C, vacuum degree of 0.3 Torr, and 9 hours. The solid phase polymerization was carried out to obtain a PET starting material A having a melting point of 255 ° C, an intrinsic viscosity of 0.80 dl/g, a terminal carboxyl group content of 10 equivalent/ton, and a Tg of 80 °C.

<PET material B>

100 parts by mass of terephthalic acid as a dicarboxylic acid component and 100 parts by mass of ethylene glycol as a diol component are used, and a polycondensation reaction is carried out using magnesium acetate, antimony trioxide or phosphorous acid as a catalyst. Then, the obtained polyethylene terephthalate was crystallized by drying at 160 ° C for 6 hours to obtain a melting point of 255 ° C, an intrinsic viscosity of 0.65 dl / g, a terminal carboxyl group amount of 25 equivalent / ton, and a Tg of 80 ° C. PET material B.

<PET material C (PET-A base titanium oxide / CHT masterbatch)>

The ratio of 5% by weight, 50% by weight, and 45% by weight of the PET raw material A obtained by the above, the rutile-type titanium oxide particles having an average particle diameter of 210 nm, and the 1,4-cyclohexanedimethylene terephthalate were respectively The mixture was mixed and melt-kneaded in an extruder at 290 ° C after the exhaust to prepare a PET-A base titanium oxide masterbatch (PET material C). Among them, in Example 6, a PET raw material C in which anatase-type titanium oxide was used without using rutile-type titanium oxide was used.

<PET material D (PET-A base titanium oxide masterbatch)>

100 parts by weight of the PET raw material A obtained above and 100 parts by weight of rutile-type titanium oxide particles having an average particle diameter of 210 nm were melt-kneaded in an extruder at 290 ° C after exhausting to prepare a PET-A base titanium oxide master batch. (PET material D).

<PET material E (PET-A substrate CHT masterbatch)>

100 parts by weight of the PET raw material A obtained above and 100 parts by weight of terephthalic acid-1,4-cyclohexanedimethyl ester were melt-kneaded in an extruder at 290 ° C after exhausting to prepare a PET-A base CHT master batch. (PET material E).

(Examples 1 to 14)

The ratio of the contents in the table (the value in the table is based on the ratio of the weight of the whole raw material to 100% by weight, the ratio of each raw material to the entire raw material) is prepared by vacuum drying at 180 ° C for 2 hours. E, and melt-kneaded in an extruder at 280 ° C, and introduced into a T-shaped nozzle.

At this time, in the first embodiment, the single layer is discharged, and in addition, the raw materials are divided. It is not melted and kneaded in two extruders, and is introduced into a T-shaped nozzle from two extruders through a feed module to obtain a P1/P2 laminate. Further, at this time, the number of screw revolutions of the two extruders was adjusted so that the laminated ratio of P1/P2 was 4/1.

Then, it is melt extruded into a sheet shape by a T-shaped nozzle, and is at a surface temperature. The cooling cylinder which was kept at 18 ° C was solidified by cooling by electrostatic application to obtain an unstretched polyester film. At this time, the rotation speed of the cooling cylinder was adjusted so that the time (residence time) in contact with the cooling cylinder was 30 seconds.

Then, the unstretched polyester film is heated to a temperature of 80 ° C. After preheating the roll group, the temperature is extended by 3 times in the longitudinal direction (longitudinal direction) by a speed difference of 3 times between the roll heated to a temperature of 88 ° C and the roll adjusted to a temperature of 25 ° C, and the temperature is 25 ° C. The roll group is cooled to obtain a uniaxially stretched polyester film. At this time, the stretching was performed at a nip of 0.5 MPa using a stretching roll having a surface roughness of 1.0 μm and a stretching nip roll.

Both ends of the uniaxially stretched polyester film obtained by gripping with a jig a preheating zone directed to the temperature of 80 ° C in the tenter, and then continuously maintained The heating zone at 90 ° C extends 3.5 times in a direction (width direction) at right angles to the longitudinal direction. Further, heat treatment was continued at 215 ° C for 20 seconds in the heat treatment zone in the tenter, and further, 7% relaxation treatment was performed in the width direction at 215 ° C. Then, gradual cooling was performed uniformly to obtain a polyester film having an overall thickness of 250 μm.

The characteristics of the obtained polyester film were evaluated, and the results are as shown in the table. Recorded.

(Examples 15 to 18)

A polyester film was obtained in the same manner as in Example 2 except that the discharge speed and the tube speed were changed to 15, 20, 120, and 125 seconds, respectively. The properties of the obtained polyester film were evaluated, and the results are shown in the table.

(Embodiment 19)

A polyester film was obtained in the same manner as in Example 2 except that the temperature of the tube was changed to 10 °C. The properties of the obtained polyester film were evaluated, and the results are shown in the table.

(Examples 20, 21, 22)

A polyester film was obtained in the same manner as in Example 2 except that the surface roughness and the extension nip of the stretching rolls at the time of uniaxial stretching were changed as described in the Table. The properties of the obtained polyester film were evaluated, and the results are shown in the table.

(Example 23)

The same procedure as in Example 2 except that the heat treatment temperature was changed to 240 °C. The method obtains a polyester film. The properties of the obtained polyester film were evaluated, and the results are as shown in the table.

(Examples 24 and 25)

A polyester film was obtained in the same manner as in Example 2 except that the relaxation rate after biaxial stretching was changed to 3% and 10%. The properties of the obtained polyester film were evaluated, and the results are shown in the table.

(Example 26)

A polyester film was obtained in the same manner as in Example 2 except that the heat treatment temperature after the biaxial stretching was changed to 200 ° C and the relaxation rate was changed to 15%. The properties of the obtained polyester film were evaluated, and the results are shown in the table.

(Examples 27 to 29)

A polyester film was obtained in the same manner as in Example 2 except that the thickness of the film was changed as described in the Table. The properties of the obtained polyester film were evaluated, and the results are shown in the table.

(Comparative examples 1 to 6, 9, 10)

A polyester film was obtained in the same manner as in Example 2 except that the temperature of the tube, the residence time, and the roll surface roughness and the extension nip when the length direction were extended were set to the conditions in the table. The properties of the obtained polyester film were evaluated, and the results are shown in the table. With respect to the films of Comparative Examples 1 to 6, 9, and 10, the thickness reduction of the film in the durability test was large, and the deterioration of the characteristics due to the durability test was large.

(Comparative Example 7)

A polyester film was obtained in the same manner as in Example 2 except that the titanium oxide was not contained in the polyester film. The properties of the obtained polyester film were evaluated, and the results are shown in the table. As a result, if titanium oxide was not added, the elongation retention rate after the durability test was largely deteriorated.

(Comparative Example 8)

A polyester film was obtained in the same manner as in Example 2 except that the thickness of the film was changed as described in the Table. The properties of the obtained polyester film were evaluated, and the results are shown in the table.

(industrial availability)

Since the polyester film of the present invention is excellent in film reduction resistance and durability, it can be preferably used for a polyester film for solar battery back sheets. A solar cell including a solar cell back sheet comprising a polyester film for a solar cell back sheet of the present invention can maintain its performance for a long period of time, and can extend the number of years of durability.

Claims (11)

A polyester film for a solar cell back sheet having a polyester layer satisfying the following (1) to (3) in at least one surface layer (this layer is referred to as a P1 layer), and a elongation retention ratio after a durability test 40% or more; (1) the thickness of the P1 layer is 30 μm or more and 250 μm or less; (2) the surface roughness (Ra) of the P1 layer is greater than 0.10 μm and is less than 0.50 μm; (3) the P1 layer after the durability test The thickness reduction is 15 μm or less; <Endurance Test> (i) Using a xenon lamp (Suga Test Instruments, SC750) under the conditions of a temperature of 65 ° C and a relative humidity of 50% RH, with a illuminance of 180 W/m ² The surface of the P1 layer side of the polyester film was irradiated for 102 minutes (t-1); (ii) after (i), while continuing to irradiate the xenon lamp, the P1 layer was sprayed at a rate of 2.1 L ± 0.1 mL/min. °C ± 5 ° C water for 18 minutes (t-2); further, let (t-1) + (t-2) = 120 minutes; (iii) repeat (i) (ii) 1500 times. A polyester film for a solar cell back sheet according to the first aspect of the invention, which comprises at least two layers of a polyester film. The polyester film for a solar cell back sheet according to the first aspect of the invention, wherein the partial discharge voltage retention rate after the durability test is 90% or more. The polyester film for a solar cell back sheet according to the first aspect of the invention, wherein the polyester resin composition constituting the P1 layer contains rutile-type titanium oxide, and the rutile-type titanium oxide content is relative to the P1 layer. The ester resin composition as a whole is 14 to 20% by weight. For example, the polyester film for solar battery back sheet of claim 1 of the patent scope, wherein The polyester resin composition in the P1 layer contains a polyester resin composition mainly composed of a 1,4-cyclohexanedimethylene terephthalate unit (hereinafter referred to as a CHT unit), and a CHT unit is mainly composed. The content of the polyester resin composition of the component is 14 to 20% by weight based on the entire polyester resin composition constituting the P1 layer. The polyester film for a solar cell back sheet according to the first aspect of the invention, wherein the polyester resin constituting the polyester film has an intrinsic viscosity of 0.6 to 1.0 dl/g and a terminal carboxyl group content of 5 to 20 equivalents/ton. A method for producing a polyester film for a solar cell back sheet according to the first aspect of the invention, which satisfies the following (4) to (6): (4) comprising the steps of: utilizing a polyester resin composition constituting the P1 layer The extruder is melt-kneaded and then extruded, and cooled and solidified on a cooling cylinder to obtain an unaligned polyester film; (5) the temperature of the cooling cylinder is Tg-70 ° C or more and Tg -30 ° C of the polyester resin constituting the P1 layer. (6) The time (staying time) in contact with the cooling cylinder is 20 seconds or more and 120 seconds or less. A method for producing a polyester film for a solar cell back sheet according to the first aspect of the invention, which satisfies the following (4), (7) to (10): (4) comprising the steps of: forming a polyester constituting the P1 layer The resin composition is melt-kneaded by an extruder, extruded, and solidified on a cooling cylinder to obtain an unaligned polyester film; (7) comprising the following steps: the unaligned polyester film obtained by (4) is oriented in the longitudinal direction The uniaxially oriented polyester film is obtained by extending at an extension temperature of 70 to 120 ° C and a stretching ratio of 2.0 to 4.0 times; (8) comprising the steps of: uniaxially aligning the polyester film obtained by the step (7) in width The direction is extended by an extension temperature of 70 to 150 ° C and a stretching ratio of 3.0 to 4.0 times. The biaxially oriented polyester film is obtained; (9) comprising the steps of: heat treating the biaxially oriented polyester film obtained by the step (8) at 205 to 240 ° C, and relaxing 0 to 10% in the width direction. (10) The extension in the above (7) is carried out by using a stretching roll and a stretching nip roll, wherein the surface roughness Ra of the stretching roll is 0.5 to 1.5 μm, and the stretching roll and the stretching nip roll are used. The nip pressure is 0.4 to 1.0 MPa. A method for producing a polyester film for a solar cell back sheet according to the first aspect of the invention, which satisfies the following (4) to (10): (4) comprising the steps of: utilizing a polyester resin composition constituting the P1 layer The extruder is melt-kneaded and then extruded, and cooled and solidified on a cooling cylinder to obtain an unaligned polyester film; (5) the temperature of the cooling cylinder is Tg-70 ° C or more and Tg -30 ° C of the polyester resin constituting the P1 layer. (6) The time (residence time) of contact with the cooling cylinder is 20 seconds or more and 120 seconds or less; (7) comprising the steps of: using the unaligned polyester film obtained by (4) in the longitudinal direction The stretching temperature is 70-120 ° C, the stretching ratio is 2.0-4.0 times to extend, and the uniaxial alignment polyester film is obtained; (8) comprising the steps of: uniaxially aligning the polyester film obtained by the step (7) in the width direction Extending at a stretching temperature of 70 to 150 ° C and a stretching ratio of 3.0 to 4.0 times to obtain a biaxially oriented polyester film; (9) comprising the steps of: the biaxially oriented polyester film obtained by the step (8) is at 205 Heat treatment at ~240 ° C, relaxing 0 to 10% in the width direction; (10) delay in (7) above And using an extension line extending in the roll nip rolls a practitioner, extending above surface roughness Ra of the roll is 0.5 ~ 1.5μm, and extending the roller clamp clip extending between the rollers The pressure is 0.4~1.0MPa. A solar battery back sheet which is a polyester film for a solar battery back sheet according to claim 1 of the patent application. A solar cell that uses the solar cell backsheet of claim 10 of the patent application.