JP5661386B2 - Polyester film and method for producing the same, solar cell backsheet, and solar cell module - Google Patents

Description

  The present invention relates to a polyester film and a production method thereof, a solar cell backsheet, and a solar cell module.

  In recent years, solar power generation as a clean energy source has attracted attention due to increasing awareness of environmental problems such as global warming, and solar cells having various forms have been developed. This solar battery is generally composed of a plurality of solar battery modules that are packaged by a plurality of solar battery cells wired in series or in parallel.

  The solar cell module is required to have high durability and weather resistance that can be used outdoors for a long period of time. As a general solar cell module, a translucent substrate made of glass or the like, a filler layer made of a thermoplastic resin such as ethylene / vinyl acetate copolymer (EVA), and a plurality of sheets as photovoltaic elements A solar battery cell, a filler layer similar to the above-described filler layer, and a back sheet are laminated in this order, and are integrally formed by a vacuum heating lamination method or the like.

  In the solar cell module, when water vapor, oxygen gas or the like enters the inside, there is a risk of peeling and discoloration of the filler layer, corrosion of the wiring, deterioration of the function of the solar cell, and the like. Therefore, the back sheet disposed in the solar cell module is required to have gas barrier properties against water vapor, oxygen gas and the like in addition to basic performance such as strength, weather resistance, and heat resistance.

  Today, in order to reduce the loss of power generation efficiency, the system voltage of the solar cell system tends to be as large as possible. In particular, recently, the demand for solar cell systems having a system voltage of 1000 V or higher has been increasing, and a high withstand voltage of about 1000 V or higher from the conventional 600 V has been required. Therefore, it is indispensable that the back sheet for the solar cell module has high voltage resistance.

  In recent years, a polyester film has been used as a back sheet for a solar cell module.

  In relation to this, from the viewpoint that strength and dimensional stability are required in applications such as solar cell backsheets, polyethylene having a film thickness of 70 μm or more and 400 μm or less is used as a relatively thick film for solar cells. A terephthalate resin film is disclosed (for example, see Patent Document 1).

  Also, a solar cell back surface protective sheet having a layer thickness of 200 μm or more formed by laminating and integrating a plurality of polyester resin layers for electrical insulation has been disclosed (for example, see Patent Document 2).

JP 2009-149065 A JP 2006-253264 A

  However, in the conventional polyethylene terephthalate-based resin film, strength and dimensional stability are required, so by improving the transverse stretching conditions (stretching zone temperature conditions) during biaxial stretching, Although heat shrinkability and processability (cutting properties and sagging) have been improved, when used as a back sheet for a solar cell for a long period of time, it tends to peel off on the solar cell, making it resistant to long-term use. There is a problem that the decomposability and insulating properties are lowered. In other words, solar cells generally have solar cells arranged on, for example, a glass substrate, and the cells are embedded with a resin (so-called sealing material) such as EVA (ethylene-vinyl acetate copolymer), and further thereon. Although it is configured to have a structure in which a back sheet is attached, hydrolysis resistance and voltage resistance are lowered and the power generation efficiency is greatly lowered when left in an environment such as outdoors exposed to wind and rain.

  Moreover, in the said solar cell back surface protection sheet which laminates | stacks a some polyester resin layer, since it is thickened by bonding, a man-hour increases and a concern of peeling remains, and it is not necessarily back sheet, EVA, etc. Peeling that tends to occur between the sealing materials cannot be avoided.

  The present invention has been made in view of the above, and is excellent in hydrolysis resistance, and is an adherend (for example, a resin material such as a sealing material for sealing a solar cell element arranged on a battery-side substrate of a solar cell module) And a manufacturing method thereof, a back sheet for solar cells, and a solar cell module having long-term durability. The goal is to achieve this.

Specific means for achieving the above object are as follows.
<1> A polyester raw material resin containing at least one selected from the group consisting of aluminum and aluminum compounds as a polymerization catalyst and having an intrinsic viscosity of 0.71 to 0.90 is discharged from an extruder (Q / N; Q Represents the extrusion rate [kg / hr] per unit time, N represents the screw rotation speed [rpm].) 50% to 80% of the theoretical maximum discharge rate, and the screw outer diameter is φ150 mm or more. An extrusion process for melt extrusion by a machine, an unstretched film forming process for forming an unstretched film by cooling and solidifying the melt-extruded polyester resin on a cast roll, and the formed unstretched film in the machine direction and the transverse direction. A polyester film having a biaxial stretching step for biaxial stretching and a heat setting step for heat fixing a stretched film formed by biaxial stretching. It is a manufacturing method.

<2> The extrusion process is the method for producing a polyester film according to <1>, wherein the extrusion is performed in a range where a maximum shear stress (σ) generated in the extruder is 1 to 1000 KPa.
<3> In the extrusion step, the oxygen concentration in the extruder is in a range of 0 to 500 ppm, and melt extrusion is performed with an average residence time in a screw compression unit and a metering unit in the extruder being 30 to 120 seconds. <1> Or it is a manufacturing method of the polyester film as described in said <2>.
<4> The method for producing a polyester film according to any one of <1> to <3>, wherein the amount of the terminal carboxylic acid group of the polyester raw material resin is 8 to 25 eq / ton or less.
<5> The polyester raw material resin is represented by the following formula: Tg-30 ° C. ≦ Temperature of polyester resin (° C.) ≦ Tg + 80 ° C.
[Tg: Glass transition temperature]
It is the manufacturing method of the polyester film as described in any one of said <1>-<4> which adjusts to the temperature range which satisfy | fills, and throws into the said extruder.

<6> In the region where the temperature of the polyester resin melt-extruded from the extruder is 140 ° C. to 230 ° C., the unstretched film forming step has an average cooling rate in the range of 230 ° C./min to 500 ° C./min. It is a manufacturing method of the polyester film as described in any one of said <1>-<5> which solidifies by cooling.
<7> The polyester raw material resin includes polyester resin recovered waste in a range of more than 0% by mass and 10% by mass or less with respect to the total mass, and the ultimate viscosity of the recovered waste and the raw resin other than the recovered waste It is a manufacturing method of the polyester film as described in any one of said <1>-<6> whose difference with a viscosity is 0.01-0.2.
<8> A polyester film produced by the method for producing a polyester film according to any one of <1> to <7>.

<9> Contains at least one selected from the group consisting of a polymerization catalyst-derived aluminum and an aluminum compound, has an intrinsic viscosity of 0.71 to 0.90, and is wet-heat treated in an atmosphere at a temperature of 120 ° C. and a relative humidity of 100%. The polyester film according to <8>, wherein the time at which the breaking elongation after the treatment is 50% with respect to the breaking elongation before the wet heat treatment is 65 to 150 hours.
<10> A solar cell backsheet comprising the polyester film according to <8> or <9>.
<11> A solar cell module comprising the polyester film according to <8> or <9>.

ADVANTAGE OF THE INVENTION According to this invention, it is excellent in hydrolysis resistance and adhesiveness with adherends (for example, resin materials, such as a sealing material which seals the solar cell element distribute | arranged to the battery side board | substrate of a solar cell module). Further, it is possible to provide a polyester film capable of maintaining the voltage resistance for a long period of time, a method for producing the same, and a back sheet for solar cells. Also,
According to the present invention, a solar cell module having long-term durability can be provided.

It is a schematic sectional drawing for demonstrating the structural example of a single screw extruder. It is a schematic sectional drawing which shows the structural example of a solar cell module.

Hereinafter, the manufacturing method of the polyester film of this invention, the polyester film using the same, the solar cell backsheet, and a solar cell module are demonstrated in detail.
In the present specification, a numerical range represented by using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.

<Polyester film and method for producing the same>
The method for producing a polyester film of the present invention comprises a polyester raw material resin containing at least one selected from the group consisting of aluminum and aluminum compounds as a polymerization catalyst and having an IV of 0.71 to 0.90. The amount (Q / N) is 50% to 80% of the theoretical maximum discharge amount, and an extrusion process in which the screw outer diameter is melt-extruded by an extruder having a diameter of φ150 mm or more, and the melt-extruded polyester resin is cooled and solidified on a cast roll. An unstretched film forming step for forming an unstretched film, a biaxial stretching step for biaxially stretching the formed unstretched film in the longitudinal direction and the transverse direction, and heating the stretched film formed by biaxial stretching. And a heat fixing step of fixing.

  In the above Q / N, Q represents the extrusion rate [kg / hr] per unit time, and N represents the screw rotation speed [rpm].

Even with the use of an aluminum-based polymerization catalyst in which a polyester having a relatively high thermal stability can be easily obtained, a relatively high IV (ultimate viscosity; = high molecular weight) of 0.71 ≦ IV ≦ 0.90 in order to improve the weather resistance When the polyester resin is melt-extruded as a raw material resin, degradation of the polyester is caused by shearing heat generated in the machine at the time of melt-extrusion, and the generated low-molecular decomposition products cause poor adhesion. Generally, the discharge amount when extruding from an extruder is set in the vicinity of the discharge capacity of the extruder, that is, the theoretical maximum discharge amount from the viewpoint of manufacturing cost, etc. If the polyester raw material resin is made to have a high IV for the purpose of increasing, shear heat generation tends to occur.
In the present invention, the discharge rate (Q / N) of the extruder at the time of melt-extrusion is 50% to 80% of the theoretical maximum required discharge rate, so that the IV is increased. At the same time, while maintaining a certain degree of discharge properties, the shear heat generation is kept small, and the adherend (for example, a resin material such as a sealing material for sealing the solar cell element disposed on the battery side substrate of the solar cell module) The adhesiveness and withstand voltage between them are maintained for a long time. In addition to preventing gelation due to reduced friction in the extruder, cooling after extrusion tends to affect the point of improving weather resistance, and in the present invention, the amount of terminal COOH (the amount of terminal carboxylic acid group) does not become too large. The molten resin is cooled and solidified on a cast roll when an unstretched film is formed after a predetermined extrusion step. That is, cooling is generally performed for the purpose of improving haze (white turbidity), but in the present invention, by cooling after extrusion, by suppressing the spherulites of the resin formed into a film, a state of high stretch orientation can be obtained. Adjusted. Thus, in the present invention, the produced polyester film is excellent in hydrolysis resistance. Show.

-Extrusion process-
The extrusion step in the present invention includes a polyester raw material resin containing at least one selected from the group consisting of aluminum and aluminum compounds as a polymerization catalyst and having an intrinsic viscosity (IV) of 0.71 to 0.90. The discharge amount (Q / N) is 50% to 80% of the theoretical maximum discharge amount, and melt extrusion is performed by an extruder having a screw outer diameter of 150 mm or more .

  In this step, a polyester resin synthesized in advance using aluminum and / or an aluminum compound as a polymerization catalyst is used as a raw material resin. The synthesis can be performed by providing an esterification step in which a polyester is produced by providing an esterification reaction and a polycondensation reaction. In this esterification step, (a) an esterification reaction and (b) a polycondensation reaction in which an esterification reaction product produced by the esterification reaction is subjected to a polycondensation reaction can be provided. Details of the esterification reaction and polycondensation reaction will be described later.

The intrinsic viscosity (IV: Intrinsic Viscosity) of the polyester film is in the range of 0.71 to 0.90. When the value of IV is within the above range, the mobility of the molecule is reduced, the formation of spherulites is suppressed, and the water content is suppressed low. Furthermore, there is also an effect of suppressing breakage (peeling) at the interface with the adherend (particularly the sealing material (for example, EVA) provided on the battery side substrate of the solar cell module) accompanying the embrittlement caused by the molecular weight reduction. If the IV is less than 0.71, spherulite formation is large, the hydrolysis resistance is poor, the brittleness and the voltage resistance are low, and conversely if the IV exceeds 0.90, shear heat generation during extrusion When the IV value is within the above range, the stretchability is good and the stretching unevenness is further suppressed.
Such an IV value can be adjusted by adjusting the polymerization time during liquid phase polymerization and / or by solid phase polymerization.

  The IV is more preferably from 0.71 to 0.85, and still more preferably from 0.72 to 0.82. As the polyester raw material resin in the present invention, a polyester resin obtained through solid phase polymerization may be used. By undergoing solid phase polymerization, the polyester resin having the IV can be used as a raw material resin. Details of the solid phase polymerization will be described later.

The intrinsic viscosity (IV) is a specific viscosity (η _sp = η _r −1) obtained by subtracting 1 from the ratio η _r (= η / η ₀ ; relative viscosity) of the solution viscosity (η) and the solvent viscosity (η ₀ ). ) Divided by the density is extrapolated to a density zero state. IV is determined from the solution viscosity at 30 ° C. in a mixed solvent of 1,1,2,2-tetrachloroethane / phenol (= 2/3 [mass ratio]).

In the present invention, the polyester raw material resin is melted by an extruder with an extruder discharge rate (Q / N) of 50% to 80% of the theoretical maximum discharge rate, that is, the filling rate inside the extruder is 50 to 80%. Extrude.
Here, the discharge amount (Q / N) of the extruder represents the discharge amount of one screw rotation. Q represents the discharge amount [cm ³ / min], and N represents the screw rotation speed [rpm].

When the discharge rate (Q / N) of the extruder is less than 50% of the theoretical maximum discharge rate, the melt component flowing backward between the barrel and flight increases, resulting in insufficient melting of the polyester resin, and the residence time becomes longer. Too much polyester degradation products, resulting in a decrease in hydrolysis resistance. On the other hand, when the Q / N of the extruder exceeds 80% of the theoretical maximum discharge amount, molecular cutting occurs due to temperature rise due to shear heat generation, the amount of terminal COOH increases, and the hydrolysis resistance is remarkably lowered.
In the present invention, by setting the Q / N with respect to the theoretical maximum discharge amount within the above range, the friction inside the extruder can be suppressed, and even when the high IV raw material resin as described above is used, the melt extrusion It is possible to suppress the shearing heat generated sometimes to such an extent that the degradation of the polyester can be reduced, and the hydrolysis resistance of the polyester can be maintained well.

The theoretical maximum discharge amount (Q / N) refers to the amount extruded per revolution when the polyester resin is filled in the extruder, and Q at this time is obtained from the following.
Q = αN− (β / η) × (dp / dl)
α: Screw propulsion flow constant N: Screw speed β: Pressure flow constant η: Average viscosity of molten resin dp / dl: Pressure gradient in screw length direction (determined by resin pressure gauge)

  Among them, the discharge amount (Q / N) is preferably in the range of 65 to 80%, more preferably in the range of 70 to 80% with respect to the theoretical maximum discharge amount.

  The temperature of the molten resin (melt) at the time of melt extrusion in the extrusion step can be in the range of 275 ° C to 300 ° C. Normally, the melt temperature is raised to maintain IV high, but in the present invention, the maximum shear stress (σ) is set within a predetermined range as described below, without significantly reducing the melt temperature. A polyester film having a low COOH amount (AV) can be obtained.

The melt extrusion can be performed using a conventionally known extruder equipped with a single screw or a twin screw for extruding a molten resin. The extruder may be a small or large apparatus. In the present invention, the screw outer diameter is φ150 mm or more (more preferably φ200 to 400 mm) from the viewpoint that the effect of improving the hydrolysis resistance of the polyester film can be further expected while suppressing shearing heat generation that is likely to occur in mass production. A single screw (single screw) or twin screw extruder is used .

The melt extrusion in the extrusion step is preferably performed in a range where the maximum shear stress (σ) generated in the extruder is 1 to 1000 KPa. By setting the maximum shear stress in the above range, it is possible to suppress the degradation of the polyester. Specifically, when the maximum shear stress is 1 KPa or more, the melt component flowing backward between the barrel and the flight is reduced, and the residence time is prolonged to some extent, so that generation of decomposition products can be prevented. Further, when the maximum shear stress is 1000 or less, the polyester molecules can be prevented from being cut, IV can be kept high, and the amount of terminal COOH (AV) can be kept low. By applying the shearing force in such a range, it is possible to promote the flow of the melt on the barrel surface and suppress the backflow.
Among the above, the maximum shear stress σ generated inside the extruder is preferably in the range of 10 to 800 KPa, more preferably in the range of 50 to 500 KPa.

The shear rate γ and the maximum shear stress σ are obtained by the following formulas (1) and (2).
γ = π · D · N / 60h (1)
σ = γ × η = (π · D · N / 60h) × η (2)
σ: Maximum shear stress [Pa]
γ: Shear rate [s ⁻¹ ]
η: Viscosity [Pa · s]
D: Screw diameter [mm]
N: Screw rotation speed [rpm]
h: Flight clearance [mm]

Said maximum shear stress (sigma) is realizable by raising moderately the back pressure in the cylinder (barrel) exit where molten resin (melt) is extruded. By increasing the back pressure, the shear stress increases due to frictional heat between the melt and the screw.
Specifically, the back pressure at the barrel outlet is preferably 1 to 30 MPa, more preferably 2 to 20 MPa, and even more preferably 3 to 15 MPa. When the back pressure is 1 MPa or more, the stirring efficiency of the melt in the barrel can be improved and the shear stress exerted on the melt can be increased uniformly more than simply increasing the rotational speed. When the back pressure is 30 MPa or less, reverse flow of the melt is prevented.

In the extrusion process, the oxygen concentration in the extruder is preferably 0 to 1000 ppm, but in the present invention, the oxygen concentration is more preferably in the range of 0 to 500 ppm. When the oxygen concentration is within the above range, oxidation of the molten resin due to residual oxygen in the extruder can be prevented. This oxygen concentration can be adjusted by carrying out in an inert (nitrogen or the like) air flow in the extruder, or while evacuating using a vented extruder.
Among these, the oxygen concentration is more preferably in the range of 0 to 300 ppm, and still more preferably in the range of 0 to 100 ppm.

Moreover, it can melt-extrude suitably by making the average residence time in the screw compression part and metering part in an extruder into 30 to 120 seconds. The region from the screw compression unit to the metering unit is the region where the temperature is highest in the extruder, and by controlling the average residence time within the above range, the effect of the screw kneading can be obtained, but the polyester Decomposition is suppressed. Specifically, when the average residence time is 30 seconds or longer, the kneading effect of the molten resin can be maintained, and when the average residence time is 120 seconds or shorter, the degradation of the polyester can be prevented.
The average residence time is more preferably 30 seconds to 100 seconds, and further preferably 40 seconds to 90 seconds.

Here, the average residence time is determined by the following formula.
Average residence time = (volume from screw compression part to measuring part [cm ³ ]) / discharge amount [cm ³ / min]

  As shown in FIG. 1, the extruder includes a cylinder (barrel) 6 having a hopper 7 for supplying a screw 5 and a raw material resin 8, and a raw material supply unit, A screw compression unit and a metering unit are provided. The screw compression portion refers to a region in the cylinder where the screw groove depth is smaller than the screw groove depth of the supply portion (for example, the screw groove depth gradually decreases from the screw groove depth of the supply portion). Thus, in the cylinder in which the screw groove depth decreases, the volume in which the resin can move (cylinder gap volume) decreases in the resin extrusion direction, and the shear stress applied to the resin increases from the screw compression section to the metering section. , Easy to fever. Therefore, in this region, the average residence time is controlled within the above range.

  By controlling the oxygen concentration and the average residence time as described above, it is possible to suppress the degradation of the polyester, suppress the phenomenon of IV decrease and AV increase, and drastically improve the hydrolysis resistance. it can.

  The amount of terminal carboxylic acid groups (AV; hereinafter referred to as terminal COOH amount or AV) of the polyester raw resin is preferably 8 to 25 eq / ton (tons) or less. By making the terminal COOH amount of the polyester resin used as the raw material resin within the above range, it is easy to keep the terminal COOH amount of the polyester film obtained after melt-extrusion low, and the hydrolysis resistance of the final film, that is, the durability is dramatically improved. Can be improved.

In the extrusion step in the present invention, the polyester raw material resin to be introduced into the hopper is previously adjusted to a temperature range satisfying the following formula and then introduced into the extruder.
Tg−30 ° C. ≦ Temperature of polyester resin ≦ Tg + 80 ° C.
In the above formula, Tg represents the glass transition temperature [° C.] of the polyester raw resin, and when multiple types of polyester are used as the raw resin, the temperature is adjusted so that each polyester satisfies the above formula with respect to each Tg. And put it in.
Thus, by heating the raw material resin before melting in the range of Tg-30 ° C. or higher, the viscosity of the raw material resin can be quickly reduced, so that the friction time during plasticization can be shortened, It is possible to reduce the shear stress and suppress the generation of shear heat. Moreover, it is possible to control the above-mentioned resin filling rate within the scope of the present invention. Furthermore, heating the raw material resin before melting is effective in reducing the amount of dissolved oxygen in the resin and reducing the oxygen concentration in the extruder. Conversely, by keeping the temperature of the raw material resin below its Tg + 80 ° C. and keeping it too high, it prevents the polyester resin from sticking to the screw part of the feed part and prevents the raw material resin from being easily screwed into the screw compression part. Can be sent to. As a result, since it is not sent to the screw compression section, it is possible to prevent deterioration due to heat.

  Among the above, the temperature of the polyester raw material resin before charging is preferably Tg-20 ° C to Tg + 70 ° C, more preferably Tg-10 ° C to Tg + 60 ° C, and further preferably Tg to Tg + 50 ° C.

In the present invention, it is preferable that the polyester raw material resin contains recovered waste of the polyester resin in a range of 10% by mass or less (over 0% by mass) with respect to the total mass. The collected waste includes a pulverized polyester, a recycled material obtained by remelting the collected polyester, and the like. Addition of recovered waste is effective in achieving the resin filling rate and the maximum shear stress σ as described above by increasing or decreasing the bulk specific gravity of the raw material resins having different shapes. Specifically, for example, two or more types of raw material resins having different sizes are mixed, or one type of polyester resin and two or more types of recovered film pulverized materials (eg, crushed debris such as film crushed chips). The bulk of the polyester raw material resin can be adjusted by a method such as mixing as a raw material resin. Thereby, it is possible to adjust a filling rate.
At this time, it is preferable that the difference between the intrinsic viscosity of the collected waste and the intrinsic viscosity of the raw material resin other than the collected waste is 0.01 to 0.2. By setting it within the range of this difference, an increase in the amount of terminal COOH can be further suppressed by suppressing heat generation during extrusion.

  Among the above, polyester recovery waste is contained in the range of 8% by mass or less (over 0% by mass) with respect to the total mass of the raw material resin, and the difference in intrinsic viscosity between the recovery waste and the raw material resin other than the recovery waste is determined. It is more preferable to set it as 0.01-0.1, More preferably, it contains the collection waste of polyester in the range of 5 mass% or less (over 0 mass%) with respect to raw material resin total mass, and collection waste and collection | recovery The difference in intrinsic viscosity with the raw material resin other than scrap is set in the range of 0.01 to 0.05.

The bulk specific gravity of the raw material resin is a specific gravity (per unit volume) obtained by dividing the mass of the powder into a predetermined shape by dividing the powder into a predetermined volume in a constant volume container, etc. Mass), and the smaller the bulk specific gravity, the larger the bulk.
In the present invention, the bulk specific gravity of the raw material resin is preferably in the range of 0.6 to 0.8. When the bulk specific gravity is 0.6 or more, melt extrusion can be performed more stably. When the bulk specific gravity is 0.8 or less, local heat generation can be effectively suppressed.

  Here, the esterification step and the solid phase polymerization step for producing the polyester raw material resin of the present invention will be described in detail.

-Esterification process-
In the esterification step, (a) an esterification reaction and (b) a polycondensation reaction in which an esterification reaction product generated by the esterification reaction is subjected to a polycondensation reaction can be provided.

(A) Esterification reaction In the esterification reaction when the polyester is polymerized, aluminum and / or an aluminum compound is used as a catalyst. Examples of the aluminum compound include aluminum salts of carboxylic acids such as aluminum acetate, basic aluminum acetate, aluminum lactate, and aluminum benzoate. Among these, basic aluminum acetate is preferable from the viewpoint of solvent solubility. Basic aluminum acetate is preferable in that it is easily dissolved in water and / or an organic solvent and has low stability and corrosiveness to metals.
Regarding the production method of basic aluminum acetate, paragraph numbers [0020] to [0054] of JP-A-2002-249558, pages 7 to 15 of international application 2002/022707, paragraph number of JP-A-2008-266359 [0031] ] To [0038].

  Further, other polycondensation catalysts such as a titanium compound, an antimony compound, a germanium compound and the like can coexist within a range in which these additions do not hinder the properties, workability, color tone and the like of the polyester. The combined use of other polycondensation catalysts is effective in improving productivity by shortening the polycondensation time.

As the amount of the basic aluminum acetate in producing the polyester, the total amount of moles of the structural units of the carboxylic acid components such as dicarboxylic acid and polyvalent carboxylic acid constituting the obtained polyester is expressed in terms of aluminum element. An amount of 0.001 to 0.05 mol% is preferable, and 0.005 to 0.02 mol% is more preferable. When the amount is 0.001 mol% or more, the catalytic activity can be satisfactorily exhibited. When the amount is 0.05 mol% or less, the thermal stability and the thermal oxidation stability are maintained. Generation of extraneous matter and increased coloring can be avoided.
The aluminum component can exhibit good catalytic activity even if the amount used is small.

  In addition to aluminum or a compound thereof, a phosphorus compound may be further used. Details of the phosphorus compound are described in paragraphs [0056] to [0178] of JP-A-2002-249558 and paragraphs [0040] to [0140] of JP-A-2008-266359. For example, by using an alkylene glycol solution of a phosphorus compound in combination with an alkylene glycol solution of aluminum or an aluminum compound, the phosphorus compound can improve the polycondensation catalyst activity and reduce the foreign matter formation attributed to the polycondensation catalyst.

  The polyester that forms the polyester film of the present invention comprises dicarboxylic acid and / or an ester-forming derivative thereof and diol and / or an ester-forming derivative thereof.

Examples of the dicarboxylic acid include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, dodecanedicarboxylic acid, tetradecanedicarboxylic acid, hexadecanedicarboxylic acid, 1,3-cyclobutanedicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 2,5-norbornanedicarboxylic acid, dimer Saturated aliphatic dicarboxylic acids such as acids or ester-forming derivatives thereof, unsaturated aliphatic dicarboxylic acids such as fumaric acid, maleic acid, itaconic acid or ester-forming derivatives thereof, orthophthalic acid, isophthalic acid, terephthalic acid, 5 -(Alkali Genus) sulfoisophthalic acid, diphenic acid, 1,3-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 4 , 4′-biphenyldicarboxylic acid, 4,4′-biphenylsulfone dicarboxylic acid, 4,4′-biphenyl ether dicarboxylic acid, 1,2-bis (phenoxy) ethane-p, p′-dicarboxylic acid, pamoic acid, anthracene Aromatic dicarboxylic acids such as dicarboxylic acids or ester-forming derivatives thereof.
Among these, terephthalic acid and naphthalenedicarboxylic acid are preferable, and 2,6-naphthalenedicarboxylic acid is particularly preferable in terms of physical properties of the obtained polyester. In this case, another dicarboxylic acid may be further used as necessary.

  In addition to these dicarboxylic acids, polyvalent carboxylic acids may be used in combination in small amounts. Examples of the polyvalent carboxylic acid include ethanetricarboxylic acid, propanetricarboxylic acid, butanetetracarboxylic acid, pyromellitic acid, trimellitic acid, trimesic acid, 3, 4, 3 ′, 4′-biphenyltetracarboxylic acid, and esters thereof. And forming derivatives.

  Moreover, you may use together hydroxycarboxylic acid. Examples of hydroxycarboxylic acids include lactic acid, citric acid, malic acid, tartaric acid, hydroxyacetic acid, 3-hydroxybutyric acid, p-hydroxybenzoic acid, p- (2-hydroxyethoxy) benzoic acid, 4-hydroxycyclohexanecarboxylic acid, or these And ester-forming derivatives thereof. Furthermore, a cyclic ester can be used in combination. Examples of the cyclic ester include ε-caprolactone, β-propiolactone, β-methyl-β-propiolactone, δ-valerolactone, glycolide, and lactide.

  Examples of ester-forming derivatives of polyvalent carboxylic acids and hydroxycarboxylic acids include alkyl esters and hydroxylalkyl esters of these compounds.

Examples of the diol include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, diethylene glycol, triethylene glycol, 1,2-butylene glycol, 1,3-butylene glycol, and 2,3-butylene glycol. 1,4-butylene glycol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 1,2-cyclohexanediol, 1,3-cyclohexanediol, 1,4-cyclohexanediol, 1,2 -Cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, 1,4-cyclohexanediethanol, 1,10-decamethylene glycol, 1,12-dodecanediol, polyethyleneglycol Aliphatic glycols such as polytrimethylene glycol and polytetramethylene glycol, hydroquinone, 4,4′-dihydroxybisphenol, 1,4-bis (β-hydroxyethoxy) benzene, 1,4-bis (β-hydroxyethoxy) Phenyl) sulfone, bis (p-hydroxyphenyl) ether, bis (p-hydroxyphenyl) sulfone, bis (p-hydroxyphenyl) methane, 1,2-bis (p-hydroxyphenyl) ethane, bisphenol A, bisphenol C, Examples include aromatic glycols such as 2,5-naphthalenediol and glycols to which ethylene oxide is added.
Of these, ethylene glycol, 1,3-propylene glycol, 1,4-butylene glycol, and 1,4-cyclohexanedimethanol are preferred.

  Examples of the ester-forming derivative of the diol include an ester of the diol with a lower aliphatic carboxylic acid such as acetic acid.

  In addition to these, a polyhydric alcohol may be used in combination if the amount is small. Examples of the polyhydric alcohol include trimethylolmethane, trimethylolethane, trimethylolpropane, pentaerythritol, glycerol, hexanetriol and the like.

  Examples of the polyester in the present invention include polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polypropylene terephthalate, poly (1,4-cyclohexanedimethylene terephthalate), polyethylene naphthalate (PEN), polybutylene naphthalate, and polypropylene naphthalate. , And their copolycondensates are preferred. Of these, polyethylene terephthalate and this copolycondensate are particularly preferred. As the copolycondensate, those having a structural unit derived from ethylene terephthalate of 50 mol% or more are preferable, and 70 mol% or more are more preferable.

(B) Polycondensation In polycondensation, an esterification reaction product generated by an esterification reaction is subjected to a polycondensation reaction to generate a polycondensation product. The polycondensation reaction may be performed in one stage or may be performed in multiple stages.

  The esterification reaction product such as an oligomer generated by the esterification reaction is subsequently subjected to a polycondensation reaction. This polycondensation reaction can be suitably performed by supplying it to a multistage polycondensation reaction tank.

For example, the polycondensation reaction conditions in the case of performing in a three-stage reaction tank are as follows: the first reaction tank has a reaction temperature of 255 to 280 ° C., more preferably 265 to 275 ° C., and a pressure of 13.3 × 10 ^−3. -1.3 × 10 ⁻³ MPa (100 to 10 torr), more preferably 6.67 × 10 ^{−3 to} 2.67 × 10 ⁻³ MPa (50 to 20 torr), wherein the second reaction tank is a reaction The temperature is 265 to 285 ° C., more preferably 270 to 280 ° C., and the pressure is 2.67 × 10 ^{−3 to} 1.33 × 10 ⁻⁴ MPa (20 to 1 torr), more preferably 1.33 × 10 ^{−. 3 to} 4.0 × 10 ⁻⁴ MPa (10 to ³ torr), and the third reaction vessel in the final reaction vessel has a reaction temperature of 270 to 290 ° C., more preferably 275 to 285 ° C., and a pressure of ^{1.33 × 10 -3 ~1.33 × 10 -5} MPa (10~0.1torr), Ri preferably embodiment is ^{6.67 × 10 -4 ~6.67 × 10 -5} MPa (5~0.5torr) are preferred.

-Solid phase polymerization process-
In the present invention, in addition to the above, a solid phase polymerization step for solid phase polymerization of polyester can be further provided. The solid-phase polymerization can be suitably performed using the polyester polymerized by the esterification reaction described above or a commercially available polyester in the form of small pieces such as pellets. The small piece shape includes chips, pellets, flakes, powdered polyester, and the like, preferably chips and pellets. The size of the small piece shape is usually 2.0 to 5.5 mm, preferably 2.2 to 5.0 mm.

  Solid-state polymerization can increase the degree of polymerization of the polyester and can reduce the amount of by-products that are by-produced during melt polymerization such as cyclic trimer, formaldehyde, and acetaldehyde. The solid-phase polymerization is carried out by converting the polyester obtained by the melt polycondensation method into small pieces (such as powder).

Solid phase polymerization can be carried out by heating a small piece of polyester at a temperature below its melting point under an inert gas flow or under reduced pressure. The step of solid phase polymerization comprises at least one stage, and the polymerization temperature is usually 190 to 235 ° C, preferably 195 to 230 ° C.
In the case of the inert gas flow method, the solid-phase polymerization is performed under the flow of an inert gas such as nitrogen, argon, carbon dioxide, etc. under a pressure of usually 0.98 MPa to 0.0013 MPa, preferably 0.49 MPa to 0.013 MPa. It is done at. In the case of the reduced pressure method, the solid phase polymerization is performed under a pressure of usually 13 to 39,000 Pa, preferably 13 to 13,300 Pa. The time for solid-phase polymerization reaches a desired physical property in a shorter time as the temperature is higher, but is usually 1 to 50 hours, preferably 5 to 30 hours, and more preferably 10 to 25 hours.
The solid phase polymerization step may be performed in multiple stages.

The polyester supplied to the solid phase polymerization step may be preliminarily crystallized by heating to a temperature lower than the temperature in the case of performing solid phase polymerization, and then may be transferred to the solid phase polymerization step.
The step of pre-crystallization may be performed by heating the polyester in the form of small pieces in a dry state usually at a temperature of 120 to 200 ° C., preferably 130 to 180 ° C. for 1 minute to 4 hours, or the polyester is subjected to a steam atmosphere. Or you may carry out by heating at the temperature of 120-200 degreeC normally for 1 minute or more in water vapor containing inert gas atmosphere or water vapor containing air atmosphere.

The melt-polycondensed polyester is supplied to a solid phase polymerization step or a storage silo by, for example, being formed into chips and then transported in a transport pipe. The transportation of such a chip causes a large amount of fine and film-like materials to be generated due to a large impact force on the surface of the chip due to a collision with the piping, etc. Therefore, it is preferable to provide a step of removing fines and film-like materials.
The process for removing the fine or film-like material is not particularly limited. For example, as an intermediate process between the solid-phase polymerization process and the post-process provided after the solid-phase polymerization process, a vibration sieve process and an air flow by an air flow are used. Examples include providing a classification process, a gravity classification process, and the like.

In addition, the polyester film is to further prevent mold contamination caused by adhesion of oligomers such as a cyclic trimer to the mold inner surface, the gas exhaust port of the mold, and the exhaust pipe at the time of molding. A contact treatment in contact with water can be provided after the solid phase polymerization. The method is not limited, and examples thereof include a method of immersing in water and a method of applying water on the chip with a shower.
The time for the contact treatment is preferably 5 minutes to 2 days, more preferably 10 minutes to 1 day, still more preferably 30 minutes to 10 hours, and the water temperature is 20 to 180 ° C., preferably 40 to 150. C., more preferably 50 to 120.degree. C. is suitable.

  Solid-phase polymerization may be carried out by a batch method (a method in which a resin is placed in a container and stirred while applying heat for a predetermined time), or a continuous method (a method in which a resin is placed in a heated cylinder). It is also possible to carry out by a method of passing through the cylinder while being kept flowing for a predetermined time while heating and sequentially sending it out. Among these, the continuous method is preferable from the viewpoint of quality uniformity and economical efficiency of the obtained polyester film.

  In the present invention, the degree of polymerization of the polyester film used as the raw material resin may be appropriately selected according to the required characteristics of the use application of the polyester, but generally 0.3 ≦ IV ≦ 0.65 by melt polycondensation. It is preferable to obtain polyester and raise the polyester obtained by melt polycondensation to 0.71 ≦ IV ≦ 0.90 by solid phase polycondensation.

  In the present invention, a color tone improving agent other than the cobalt compound can be used to improve the color tone of the polyester. The color tone improving agent is a substance that can change the color tone when added. The color tone improving agent is not particularly limited, but inorganic and organic pigments, dyes, fluorescent whitening agents and the like are preferable.

  When using a pigment or dye, the brightness of the polycondensate tends to decrease as the content increases. Therefore, when using pigments and dyes, the total content of these is preferably 20 ppm or less, more preferably 10 ppm or less, and even more preferably 5 ppm or less with respect to the resulting polyester. In this region, the coloration can be effectively eliminated without reducing the brightness of the polycondensate.

In addition, it is preferable to use a fluorescent brightening agent alone or in combination with another color tone improving agent in order to improve the color tone, for example, to reduce the amount of pigment or dye. Conventionally known fluorescent whitening agents can be used alone or in combination. Specific examples of the fluorescent brightener include benzoxazoline-based fluorescent brighteners. Particularly preferred optical brighteners include UVITEX OB, UVITEX OB-P, UVITEX OB-ONE manufactured by Ciba Specialty Chemicals, HOSTALUX KS manufactured by Clariant, and those described in JP-A-10-1563. It is done.
The fluorescent whitening agent can be used in the range of 50 ppm or less with respect to the obtained polyester, and the range of 5 to 25 ppm is more preferable.

The inorganic pigment is not particularly limited as long as the color tone can be changed. For example, titanium dioxide, carbon black, iron black, nickel titanium yellow, yellow iron oxide, cadmium yellow, chrome lead, chrome titanium yellow, zinc ferrite pigment , Petals, cadmium red, molybdenum red, chromium oxide, spinel green, chrome orange, cadmium orange, ultramarine, bitumen, cobalt blue, and the like. Among these, chromium oxide, ultramarine blue, bitumen, and cobalt blue are preferable, and ultramarine blue and cobalt blue are more preferable.
The details of organic pigments and dyes can be referred to the descriptions in paragraphs [0162] to [0165] of International Application 2002/022707, pages 10 to 11 and JP-A-2008-266359. Further, a dispersant may be used for dispersibility of pigments and the like. Details of the dispersant are described in International Application 2002/022707, page 11, paragraph No. [0168] of JP 2008-266359 A. Has been.

-Unstretched film formation process-
The unstretched film formation process in this invention forms an unstretched film by cooling and solidifying the polyester resin melt-extruded by the said extrusion process on a cast roll (cooling roll).

The molten resin (melt) discharged in a band shape is cooled and solidified on a cast roll to obtain a polyester film having a desired thickness. At this time, the film thickness before stretching is preferably in the range of 2600 μm to 6000 μm. Within this range, a polyester film having a thickness of 260 μm or more and 500 μm or less can be obtained through subsequent stretching.
The thickness of the melt after solidification is preferably in the range of 3100 μm to 6000 μm, more preferably 3300 μm to 5000 μm, and still more preferably 3500 μm to 4500 μm. When the thickness after solidification and before stretching is 6000 μm or less, wrinkles are unlikely to occur during melt extrusion, and unevenness is suppressed. Moreover, a favorable withstand voltage characteristic is acquired because the thickness after solidification is 2600 micrometers or more.

When the molten resin extruded from the extruder in the extrusion step is cast on a cast roll, the average cooling rate in the temperature range of 140 ° C. to 230 ° C. of the molten resin is in the range of 230 ° C./min to 500 ° C./min. It is preferable that A high draw ratio is required for improving weather resistance, and therefore, from the viewpoint of suppressing spherulite, the average cooling rate is preferably within the above range. Here, the average cooling rate is an average cooling rate between 140 ° C. and 230 ° C. that has the greatest influence on crystal formation, crystallization associated with spherulite formation and the like is suppressed, and weather resistance is further improved. be able to.
When the average cooling rate is 230 ° C./min or more, crystallization associated with spherulite formation or the like is suppressed, and even if the film is stretched at a high stretch ratio, the film is hardly broken and a highly oriented stretched film can be obtained. Moreover, by suppressing the formation of spherulites, the stretching unevenness is greatly reduced, and unevenness is less likely to occur when applied in the solar cell application described below. Thus, the hydrolysis resistance of the polyester film is significantly improved, and poor adhesion of the film can be suppressed by suppressing spherulite. Further, when the average cooling rate is 500 ° C./min or less, rapid solidification of the melt can be prevented, and it is possible to prevent stretching unevenness and poor adhesion due to generation of flaws on the cast roll.

  As said average cooling rate, 280-500 degreeC / min is more preferable, More preferably, it is 300-450 degreeC / min.

The average cooling rate can be adjusted and realized by the following method.
(1) Adjust the cooling air volume and cooling air temperature.
(2) Thickness unevenness of 0.1% to 5% (preferably 0.2% to 3%, more preferably 0.3% to 2%) is given to the molten resin (melt). Thereby, the adhesion to the cooling roll is improved, the cooling efficiency is improved, and it is possible to adjust to the range of the average cooling rate. This is because the melt shrinks when coming into contact with the cooling roll, but if the thickness is slightly uneven as described above, the melt can be smoothly shrunk on the cooling roll and uniformly brought into contact with the cooling roll. Therefore, it is considered that the cooling efficiency is improved. In other words, when there is no thickness unevenness, the slip of the melt tends to decrease, some stick to the cooling roll, and the other part is stretched between the sticking points (due to shrinkage stress) and cannot contact the cooling roll. It is presumed that the cooling rate will decrease.
When the thickness unevenness is 5% or less, the cooling efficiency does not increase excessively and spherulite formation is maintained to some extent, so that the effect of improving film strength by spherulite is obtained. Moreover, the adhesive force fall by the cohesive failure in a film can be prevented because it is 0.1% or more.

  The unmelted material (foreign matter) in the molten resin (melt) is preferably 0.1 piece / kg or less. Spherulites are easily formed with the unmelted material in the melt as the core, but the amount of unmelted material (foreign matter) is 0.1 piece / kg or less to suppress the formation of spherulites, and uneven stretching during stretching Occurrence can be further suppressed. Note that the unmelted material (foreign matter) is a crystal or an insoluble material that is decomposed and generated, and this foreign matter has a size of 1 μm or more and 10 mm or less.

  The amount of unmelted material is more preferably 0.005 / kg or more and 0.07 / kg or less in the molten resin (melt), more preferably 0.01 / kg or more and 0.000 or less. It is 05 pieces / kg or less. Unmelted matter (foreign matter) is obtained by taking an enlarged image of a polyester film using a phase contrast microscope and a CCD camera and counting the number of foreign matters using an image processing apparatus.

-Biaxial stretching process-
In the biaxial stretching step in the present invention, the unstretched film formed in the unstretched film forming step is biaxially stretched in the longitudinal direction and the transverse direction.
Specifically, the unstretched polyester film is led to a group of rolls heated to a temperature of 70 ° C. or higher and 140 ° C. or lower, and stretched by 3 times or more and 5 times or less in the longitudinal direction (longitudinal direction, that is, the traveling direction of the film). The film is preferably stretched at a rate and cooled with a roll group having a temperature of 20 ° C. or higher and 50 ° C. or lower. Subsequently, the film is guided to a tenter while gripping both ends of the film with a clip, and in an atmosphere heated to a temperature of 80 ° C. or higher and 150 ° C. or lower, the direction perpendicular to the longitudinal direction (width direction) is 3 to 5 times. Stretch at a stretch ratio.

  The stretching ratio is preferably 3 to 5 times in each of the longitudinal direction and the width direction. Moreover, it is preferable that the area magnification (longitudinal stretch magnification x lateral stretch magnification) is 9 times or more and 15 times or less. When the area magnification is 9 times or more, the reflectivity, concealability and film strength of the obtained biaxially stretched laminated film are good, and when the area magnification is 15 times or less, tearing during stretching should be avoided. Can do.

  As the biaxial stretching method, as described above, in addition to the sequential biaxial stretching method in which the longitudinal direction and the width direction are separated separately, the simultaneous biaxial stretching method in which the longitudinal direction and the width direction are simultaneously stretched. Either may be sufficient.

  In order to complete the crystal orientation of the obtained biaxially stretched film and to impart flatness and dimensional stability, the melting point (Tm) above the glass transition temperature (Tg) of the resin, which is preferably the raw material, is preferably continued in the tenter. ) Heat treatment is carried out at a temperature lower than 1 second and not longer than 30 seconds, uniformly cooled gradually, and then cooled to room temperature. In general, when the heat treatment temperature (Ts) is low, the thermal contraction of the film is large. Therefore, in order to impart high thermal dimensional stability, the heat treatment temperature is preferably higher. However, if the heat treatment temperature is too high, the orientation crystallinity is lowered, and as a result, the formed film may be inferior in hydrolysis resistance. Therefore, the heat treatment temperature (Ts) of the polyester film of the present invention is preferably 40 ° C. ≦ (Tm−Ts) ≦ 90 ° C. More preferably, the heat treatment temperature (Ts) is 50 ° C. ≦ (Tm−Ts) ≦ 80 ° C., more preferably 55 ° C. ≦ (Tm−Ts) ≦ 75 ° C.

  Furthermore, although the polyester film of the present invention can be used as a back sheet constituting a solar cell module, the ambient temperature may rise to about 100 ° C. when the module is used. For this reason, the heat treatment temperature (Ts) is preferably 160 ° C. or higher and Tm−40 ° C. (however, Tm−40 ° C.> 160 ° C.) or lower. More preferably, it is 170 degreeC or more and Tm-50 degreeC (however, Tm-50 degreeC> 170 degreeC), More preferably, Ts is 180 degreeC or more and Tm-55 degreeC (however, Tm-55 degreeC> 180 degreeC) or less.

  Moreover, you may perform a 3-12% relaxation process in the width direction or a longitudinal direction as needed.

-Heat setting process-
In the heat setting step in the present invention, the stretched film formed by biaxial stretching in the biaxial stretching step is heat-set.
The heat setting can be suitably performed at a temperature of 180 ° C. or higher and 240 ° C. or lower. When the temperature at the time of heat setting is 180 ° C. or more, it is preferable in that the absolute value of the heat shrinkage rate is small, and conversely, when the temperature at the time of heat setting is 240 ° C. or less, the film hardly becomes opaque and the frequency of breakage Is preferable in that it decreases.
In this case, the heat setting time is preferably 2 to 60 seconds, more preferably 3 to 40 seconds, and further preferably 4 to 30 seconds.

Generally, the film after stretching is heat-fixed by a heat-fixing apparatus in which a plurality of plenum ducts having a long hot air outlet are arranged perpendicular to the longitudinal direction. In such a heat fixing apparatus, hot air is circulated in order to improve heating efficiency. Air in the heat fixing device is sucked by a circulation fan attached to the heat fixing device, the temperature of the sucked air is adjusted, and the air is again discharged from the hot air outlet of the plenum duct. In this way, hot air circulation such as hot air blowing → suction by a circulating fan → temperature adjustment of sucked air → hot air blowing is performed.
The heat setting during film production includes (1) adjusting the temperature and air volume of the plenum duct of the heat fixing device, (2) adjusting the shut-off conditions of the hot air outlet of the plenum duct of the heat fixing device, and (3) the stretching zone and It can be suitably performed by interrupting the heating with the heat fixing device.

In (1) above, in order to perform heating and cooling step by step, the heat setting device is generally divided into several heat setting zones having different temperatures, and the temperature difference and the wind speed difference between adjacent heat setting zones. It is preferable to adjust the temperature and the air volume of the hot air blown out from each plenum duct so that the product of the two is 250 ° C. · m / s or less. For example, when the heat setting device is divided into first to third heat setting zones, the product of the temperature difference between the first zone and the second zone and the wind speed difference, the temperature difference between the second zone and the third zone. It is preferable that both of the product of the wind speed difference and the wind speed difference be adjusted to 250 ° C. · m / s or less. By adjusting the temperature and air volume of the hot air, the hot air is circulated smoothly. As a result, a film having good flatness can be obtained even by heat fixation at a high temperature. The product of the temperature difference and the wind speed difference between adjacent heat setting zones is 250 ° C. · m / s or less (for example, the temperature difference between adjacent heat setting zones is set to 20 ° C. and adjacent heat setting When the wind speed difference between the zones is set to 10 m / s), the circulation of the hot air in the heat fixing device becomes smooth. In addition, if the product of the temperature difference between the adjacent heat setting zones and the difference in wind speed is 250 ° C. · m / s or less, the accompanying heat generated by the passage of the film from the upstream heat setting zone to the downstream heat setting zone And the temperature difference between the air flowing in becomes smaller. Therefore, it is preferable in that the temperature in the width direction of the downstream heat setting zone is stabilized. The product of the temperature difference and the wind speed difference is preferably 200 ° C. · m / s or less, and more preferably 150 ° C. · m / s or less.
For details of the above (2) and (3), reference can be made to the description of paragraph numbers [0081] to [0082] of JP2009-149065.

In addition to the above heat setting, the film shrinkage in the film longitudinal direction can be further reduced to reduce the thermal contraction rate of the film edge. That is, in the relaxation process in the longitudinal direction of the film, by providing a bendable structure between the clips and adjusting the clip interval in the longitudinal direction, the interval in the moving direction of the clip contracts and the longitudinal direction is relaxed. The relaxation rate is preferably 1% or more and 8% or less, and more preferably 1.5% or more and 7.0% or less. For such a method, reference can be made to the description in paragraph [0085] of JP-A-2009-149065.
As temperature (thermal relaxation temperature) at the time of heat relaxation, 170 to 240 degreeC is preferable and 180 to 230 degreeC is more preferable.

The polyester film of the present invention is produced by the above-described method for producing a polyester film of the present invention.
The polyester film of the present invention is obtained using aluminum and / or an aluminum compound as a polymerization catalyst. Aluminum and / or an aluminum compound can produce a polyester having good thermal stability. The details of aluminum and / or aluminum compound are as described in detail in the method for producing the polyester film. Aluminum and / or aluminum compounds are preferably contained in the film in the range of 1 ppm to 50 ppm. More preferably, it is the range of 2 ppm or more and 30 ppm or less, More preferably, it is the range of 2 ppm or more and 15 ppm or less.

  The hydrolysis resistance of the polyester film can be evaluated by the retention time at breaking elongation. This is calculated | required from the fall of the breaking elongation at the time of promoting hydrolysis by heat-processing (thermo process) forcibly. A specific measuring method is shown below.

In the polyester film of the present invention, the thickness after stretching is preferably in the range of 125 μm or more and 500 μm or less from the viewpoint of imparting high withstand voltage characteristics within a practical thickness range. In order to provide a high withstand voltage of 1000 V or more, which has recently been required as a withstand voltage characteristic of the polyester film, the thickness after stretching is preferably in the range of 180 μm or more and 400 μm or less. In addition, a decrease in hydrolysis resistance can be suppressed to a small extent. The withstand voltage can be maintained when the thickness is 125 μm or more. Conversely, a thickness exceeding 500 μm is not practical.
Among the above, the thickness of the stretched polyester film is preferably in the range of 150 μm to 380 μm, and more preferably in the range of 180 μm to 350 μm.

  The said withstand voltage is a value calculated | required by measuring the voltage value at the time of destruction (it short-circuits) according to JIS specification C2151.

The polyester film of the present invention preferably has a break elongation retention time of 65 to 150 hours [h]. When the breaking elongation holding time is 65 hours or longer, the progress of hydrolysis is suppressed as described above, and peeling and poor adhesion can be prevented. In addition, when the elongation at break is 150 hours or less, the film moisture content is reduced, so that the crystal structure is prevented from developing excessively, and the elastic modulus and tensile stress are kept to such an extent that peeling does not occur. Can do.
Among them, a preferable breaking elongation retention time is 80 to 150 hours, and more preferably 90 to 150 hours.
In the present invention, it is preferable to increase the film thickness as described above. However, increasing the film thickness directly leads to an improvement in moisture content and a decrease in hydrolysis resistance, and simply increasing the thickness to 260 μm or more results in dimensional stability and hydrolysis resistance. The desired long-term durability cannot be obtained. When the breaking elongation retention time is in the above range, embrittlement accompanying hydrolysis of the polyester film is suppressed, and a decrease in adhesion due to cohesive failure in the film during adhesion can be suppressed.

The breaking elongation retention time is a breaking elongation at which the breaking elongation retention rate after wet heat treatment (thermo treatment) at 120 ° C. and 100% RH can be maintained in a range of 50% or more with respect to the breaking elongation before wet heat treatment. Degree half time [hr]. The breaking elongation retention is obtained by the following formula.
Breaking elongation retention [%] = (breaking elongation after thermo treatment) / (breaking elongation before thermo treatment) × 100

  Specifically, after performing heat treatment (thermo treatment) at 120 ° C. and 100% RH for 10 hours to 300 hours [hr] at intervals of 10 hours, the elongation at break of each thermo-treated sample was measured and obtained. The measured value is divided by the breaking elongation before the thermo treatment to obtain the breaking elongation retention ratio at each thermo treatment time. Then, the abscissa represents the thermo time, and the ordinate represents the breaking elongation retention, and the results are connected to determine the treatment time [hr] until the breaking elongation retention reaches 50% or more.

  The elongation at break is set in the MD direction (longitudinal direction; Machine Direction) by setting a polyester film sample in a tensile tester and pulling at 20 mm / min in an environment of 25 ° C. and 60% RH. ) And the TD direction (transverse direction), a value obtained by measuring 50 points at 20 cm intervals at each point divided equally into 10 in the width direction and averaging the obtained values. It is. The difference between the maximum value and the minimum value of the 50-point breaking elongation retention time obtained above (absolute value) is divided by the average value of the 50-point breaking elongation and expressed as a percentage, thereby maintaining the breaking elongation. A time distribution [%] can be obtained.

  The polyester film in the present invention can further contain additives such as a light stabilizer and an antioxidant.

  The polyester film of the present invention preferably contains a light stabilizer. By containing the light stabilizer, it is possible to prevent ultraviolet degradation. Examples of the light stabilizer include a compound that absorbs light such as ultraviolet rays and converts it into thermal energy, a material that absorbs light and decomposes when the film or the like absorbs light, and a material that suppresses the decomposition chain reaction. .

  The light stabilizer is preferably a compound that absorbs light such as ultraviolet rays and converts it into heat energy. By including such a light stabilizer in the film, it becomes possible to keep the effect of improving the partial discharge voltage by the film high for a long time even if the film is irradiated with ultraviolet rays continuously for a long time. Changes in color tone, strength deterioration, and the like due to UV rays. For example, if an ultraviolet absorber is a range in which other properties of the polyester are not impaired, any of organic ultraviolet absorbers, inorganic ultraviolet absorbers, and combinations thereof are preferably used without particular limitation. Can do. On the other hand, it is desired that the ultraviolet absorber is excellent in moisture and heat resistance and can be uniformly dispersed in the film.

Examples of the ultraviolet absorber include salicylic acid-based, benzophenone-based, benzotriazole-based, cyanoacrylate-based ultraviolet absorbers, hindered amine-based ultraviolet stabilizers, and the like as organic ultraviolet absorbers. Specifically, for example, salicylic acid-based pt-butylphenyl salicylate, p-octylphenyl salicylate, benzophenone-based 2,4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-methoxy -5-sulfobenzophenone, 2,2 ', 4,4'-tetrahydroxybenzophenone, bis (2-methoxy-4-hydroxy-5-benzoylphenyl) methane, benzotriazole 2- (2'-hydroxy-5) '-Methylphenyl) benzotriazole, 2- (2'-hydroxy-5'-methylphenyl) benzotriazole, 2,2'-methylenebis [4- (1,1,3,3-tetramethylbutyl) -6 (2H benzotriazol-2-yl) phenol], a cyanoacrylate Ethyl-2-cyano-3,3′-diphenylacrylate), 2- (4,6-diphenyl-1,3,5-triazin-2-yl) -5-[(hexyl) oxy] -phenol as triazine system Hindered amine-based bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate, dimethyl succinate 1- (2-hydroxyethyl) -4-hydroxy-2,2,6,6-tetramethyl Piperidine polycondensate, in addition, nickel bis (octylphenyl) sulfide, 2,4-di-t-butylphenyl-3 ′, 5′-di-t-butyl-4′-hydroxybenzoate, and the like .
Of these ultraviolet absorbers, triazine-based ultraviolet absorbers are more preferable in that they have high resistance to repeated ultraviolet absorption. In addition, these ultraviolet absorbers may be added to the above-mentioned ultraviolet absorber alone, or a form in which an organic conductive material or a water-insoluble resin is copolymerized with a monomer having an ultraviolet absorber ability. May be introduced.

  The content of the light stabilizer in the polyester film is preferably 0.1% by mass or more and 10% by mass or less, and more preferably 0.3% by mass or more and 7% by mass or less with respect to the total mass of the polyester film. More preferably, it is 0.7 mass% or more and 4 mass% or less. Thereby, the molecular weight fall of the polyester by the photodegradation over a long time can be suppressed, and the adhesive force fall resulting from the cohesive failure in the film which arises as a result can be suppressed.

  In addition to the light stabilizer, the polyester film of the present invention includes, for example, a lubricant (fine particles), an ultraviolet absorber, a colorant, a heat stabilizer, a nucleating agent (crystallization agent), and a flame retardant. Etc. can be contained as additives.

<Back sheet for solar cell>
The back sheet for a solar cell of the present invention is configured by providing the polyester film of the present invention as described above, and has an easy-adhesive layer, an ultraviolet absorbing layer, and a light-reflecting property that are easily adhered to an adherend. It can be configured by providing at least one functional layer such as a white layer. Since the polyester film described above is provided, stable durability is exhibited during long-term use.

In the solar cell backsheet of the present invention, for example, the following functional layer may be applied to a polyester film after uniaxial stretching and / or biaxial stretching. For coating, a known coating technique such as a roll coating method, a knife edge coating method, a gravure coating method, or a curtain coating method can be used.
Further, surface treatment (flame treatment, corona treatment, plasma treatment, ultraviolet treatment, etc.) may be performed before the coating. Furthermore, it is also preferable to bond together using an adhesive.

-Easy adhesive layer-
The polyester film of the present invention has an easy-adhesive layer on the side facing the sealing material of the battery-side substrate in which the solar cell element is sealed with a sealing agent when constituting a solar cell module. Is preferred. Easy adhesion showing adhesion to an adherend containing a sealing agent (particularly ethylene-vinyl acetate copolymer) (for example, the surface of the sealing agent on the battery side substrate in which the solar cell element is sealed with the sealing material). By providing the conductive layer, the back sheet and the sealing material can be firmly bonded. Specifically, it is preferable that the easy-adhesive layer has an adhesive force of 10 N / cm or more, preferably 20 N / cm or more, particularly with EVA (ethylene-vinyl acetate copolymer) used as a sealing material.
Further, the easy-adhesive layer needs to prevent the backsheet from peeling off during use of the solar cell module, and therefore, the easy-adhesive layer desirably has high moisture and heat resistance.

(1) Binder The easy-adhesive layer in the present invention can contain at least one binder.
As the binder, for example, polyester, polyurethane, acrylic resin, polyolefin, or the like can be used. Among these, acrylic resins and polyolefins are preferable from the viewpoint of durability. As the acrylic resin, a composite resin of acrylic and silicone is also preferable. The following can be mentioned as an example of a preferable binder.
Examples of the polyolefin include Chemipearl S-120 and S-75N (both manufactured by Mitsui Chemicals, Inc.). Examples of the acrylic resin include Julimer ET-410 and SEK-301 (both manufactured by Nippon Pure Chemical Industries, Ltd.). Examples of the composite resin of acrylic and silicone include Ceranate WSA 1060 and WSA 1070 (both manufactured by DIC Corporation), and H7620, H7630, and H7650 (both manufactured by Asahi Kasei Chemicals Corporation).
The amount of the binder is preferably in the range of 0.05-5 g / ^{m 2,} the range of 0.08~3g / ^{m 2} is particularly preferred. The binder amount is more good adhesion is obtained by at 0.05 g / m ² or more, a better surface is obtained by at 5 g / m ² or less.

(2) Fine particles The easy-adhesion layer in the present invention can contain at least one kind of fine particles. The easy-adhesive layer preferably contains 5% by mass or more of fine particles with respect to the mass of the entire layer.
As the fine particles, inorganic fine particles such as silica, calcium carbonate, magnesium oxide, magnesium carbonate, tin oxide and the like are preferably exemplified. Among these, fine particles of tin oxide and silica are preferable in that the decrease in adhesiveness when exposed to a humid heat atmosphere is small.
The particle size of the fine particles is preferably about 10 to 700 nm, more preferably about 20 to 300 nm. By using fine particles having a particle diameter in the above range, good easy adhesion can be obtained. The shape of the fine particles is not particularly limited, and those having a spherical shape, an indefinite shape, a needle shape, or the like can be used.
The addition amount of the fine particles in the easy-adhesive layer is preferably 5 to 1000% by mass, more preferably 5 to 400% by mass, and still more preferably 50 to 300% by mass per binder in the easy-adhesive layer. When the addition amount of the fine particles is 5% by mass or more, the adhesiveness when exposed to a moist heat atmosphere is excellent, and when it is 1000% by mass or less, the surface state of the easy-adhesive layer is better.

(3) Crosslinking agent The easy-adhesion layer in this invention can contain at least 1 sort (s) of a crosslinking agent.
Examples of the crosslinking agent include epoxy-based, isocyanate-based, melamine-based, carbodiimide-based, and oxazoline-based crosslinking agents. Among these, an oxazoline-based cross-linking agent is particularly preferable from the viewpoint of securing adhesiveness after wet heat aging.
Specific examples of the oxazoline-based crosslinking agent include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline. 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-ethyl-2-oxazoline, 2,2′-bis- (2-oxazoline), 2,2′-methylene-bis- ( 2-oxazoline), 2,2′-ethylene-bis- (2-oxazoline), 2,2′-trimethylene-bis- (2-oxazoline), 2,2′-tetramethylene-bis- (2-oxazoline) 2,2′-hexamethylene-bis- (2-oxazoline), 2,2′-octamethylene-bis- (2-oxazoline), 2,2′-ethylene-bis- (4,4′- Methyl-2-oxazoline), 2,2'-p-phenylene-bis- (2-oxazoline), 2,2'-m-phenylene-bis- (2-oxazoline), 2,2'-m-phenylene- Bis- (4,4′-dimethyl-2-oxazoline), bis- (2-oxazolinylcyclohexane) sulfide, bis- (2-oxazolinylnorbornane) sulfide and the like can be mentioned. Furthermore, (co) polymers of these compounds can also be preferably used.
Further, as a compound having an oxazoline group, Epocros K2010E, K2020E, K2030E, WS500, WS700 (all manufactured by Nippon Shokubai Co., Ltd.) and the like can be used.
The preferable addition amount of the crosslinking agent in the easy-adhesive layer is preferably 5 to 50% by mass, more preferably 20 to 40% by mass per binder of the easy-adhesive layer. When the addition amount of the crosslinking agent is 5% by mass or more, a good crosslinking effect is obtained, and the strength of the reflective layer is not reduced and adhesion failure hardly occurs, and when it is 50% by mass or less, the pot life of the coating liquid is further increased. I can keep it long.

(4) Additives In the easy-adhesive layer in the present invention, a known matting agent such as polystyrene, polymethyl methacrylate, or silica, or a known surfactant such as an anionic or nonionic surfactant is added as necessary. May be.

(5) Method for forming easy-adhesive layer As a method for forming the easy-adhesive layer of the present invention, there are a method for bonding a polymer sheet having easy adhesion to a polyester film and a method for coating. It is preferable in that it can be formed with a simple and highly uniform thin film. As a coating method, for example, a known method such as a gravure coater or a bar coater can be used. The solvent of the coating solution used for coating may be water or an organic solvent such as toluene or methyl ethyl ketone. A solvent may be used individually by 1 type and may be used in mixture of 2 or more types.

(6) Physical property Although there is no restriction | limiting in particular in the thickness of the easily-adhesive layer in this invention, Usually, 0.05-8 micrometers is preferable, More preferably, it is the range of 0.1-5 micrometers. When the thickness of the easy-adhesive layer is 0.05 μm or more, the required easy adhesion can be easily obtained, and when the thickness is 8 μm or less, the planar shape can be maintained better.
In addition, the easy-adhesion layer in the present invention may have transparency from the viewpoint of not impairing the effect of the colored layer when a colored layer (particularly a reflective layer) is disposed between the polyester film. preferable.

-UV absorbing layer-
The polyester film of the present invention may be provided with an ultraviolet absorbing layer containing the above ultraviolet absorber. An ultraviolet absorption layer can be arrange | positioned in the arbitrary positions on a polyester film.
The ultraviolet absorber is preferably dissolved and dispersed together with an ionomer resin, polyester resin, urethane resin, acrylic resin, polyethylene resin, polypropylene resin, polyamide resin, vinyl acetate resin, cellulose ester resin, and the like. The transmittance is preferably 20% or less.

-Colored layer-
The polyester film of the present invention can be provided with a colored layer. The colored layer is a layer arranged in contact with the surface of the polyester film or through another layer, and can be constituted using a pigment or a binder.

  The first function of the colored layer is to increase the power generation efficiency of the solar cell module by reflecting the light that has reached the back sheet without being used for power generation in the solar cell out of the incident light and returning it to the solar cell. is there. The second function is to improve the decorativeness of the appearance when the solar cell module is viewed from the front side. In general, when a solar cell module is viewed from the front side, a back sheet can be seen around the solar cell, and the decorativeness can be improved by providing a colored layer on the back sheet.

(1) Pigment The colored layer in the present invention can contain at least one pigment. The pigment is preferably contained in the range of 2.5 to 8.5 g / m ² . A more preferable pigment content is in the range of 4.5 to 7.5 g / m ² . When the pigment content is 2.5 g / m ² or more, necessary coloring can be easily obtained, and the light reflectance and decorativeness can be adjusted to be more excellent. When the pigment content is 8.5 g / m ² or less, the planar shape of the colored layer can be maintained better.

  Examples of the pigment include inorganic pigments such as titanium oxide, barium sulfate, silicon oxide, aluminum oxide, magnesium oxide, calcium carbonate, kaolin, talc, ultramarine blue, bitumen, and carbon black, and organic pigments such as phthalocyanine blue and phthalocyanine green. It is done. Among these pigments, a white pigment is preferable from the viewpoint of constituting a colored layer as a reflective layer that reflects incident sunlight. As the white pigment, for example, titanium oxide, barium sulfate, silicon oxide, aluminum oxide, magnesium oxide, calcium carbonate, kaolin, talc and the like are preferable.

As an average particle diameter of a pigment, 0.03-0.8 micrometer is preferable, More preferably, about 0.15-0.5 micrometer is preferable. If the average particle size is within the above range, the light reflection efficiency may be reduced.
When a colored layer is configured as a reflective layer that reflects incident sunlight, the preferred addition amount of the pigment in the reflective layer varies depending on the type of pigment used and the average particle size, but cannot be generally stated. preferably to 15 g / ^{m 2,} more preferably about 3 to 10 g / ^{m 2.} When the addition amount is 1.5 g / m ² or more, the required reflectance is easily obtained, and when the addition amount is 15 g / m ² or less, the strength of the reflection layer can be kept higher.

(2) Binder The colored layer in the present invention can contain at least one binder. As a quantity in case a binder is included, the range of 15-200 mass% is preferable with respect to the said pigment, and the range of 17-100 mass% is more preferable. When the amount of the binder is 15% by mass or more, the strength of the colored layer can be more favorably maintained, and when it is 200% by mass or less, the reflectance and the decorativeness are lowered.
As a binder suitable for the colored layer, for example, polyester, polyurethane, acrylic resin, polyolefin, or the like can be used. From the viewpoint of durability, the binder is preferably an acrylic resin or a polyolefin. As the acrylic resin, a composite resin of acrylic and silicone is also preferable. Examples of preferred binders include the following.
Examples of the polyolefin include Chemipearl S-120 and S-75N (both manufactured by Mitsui Chemicals). Examples of the acrylic resin include Julimer ET-410 and SEK-301 (both manufactured by Nippon Pure Chemical Industries, Ltd.). Examples of the composite resin of acrylic and silicone include Ceranate WSA1060, WSA1070 (both manufactured by DIC Corporation), H7620, H7630, H7650 (both manufactured by Asahi Kasei Chemicals Corporation) and the like.

(3) Additive In addition to the binder and the pigment, a cross-linking agent, a surfactant, a filler, and the like may be further added to the colored layer in the present invention as necessary.

  Examples of the crosslinking agent include epoxy-based, isocyanate-based, melamine-based, carbodiimide-based, and oxazoline-based crosslinking agents. The addition amount of the crosslinking agent in the colorant is preferably 5 to 50% by mass, more preferably 10 to 40% by mass, per binder of the colored layer. When the addition amount of the crosslinking agent is 5% by mass or more, a good crosslinking effect can be obtained, the strength and adhesiveness of the colored layer can be maintained high, and when it is 50% by mass or less, the coating solution The pot life can be maintained longer.

As the surfactant, a known surfactant such as an anionic or nonionic surfactant can be used. 0.1-15 mg / m < ² > is preferable and, as for the addition amount of surfactant, 0.5-5 mg / m < ² > is more preferable. The amount of the surfactant added is 0.1 mg / m ² or more to effectively suppress the occurrence of repelling, and the addition amount of 15 mg / m ² or less provides excellent adhesion.

  Furthermore, a filler such as silica may be added to the colored layer in addition to the above pigment. The addition amount of the filler is preferably 20% by mass or less, more preferably 15% by mass or less per binder of the colored layer. By including the filler, the strength of the colored layer can be increased. Moreover, since the ratio of a pigment can be maintained because the addition amount of a filler is 20 mass% or less, favorable light reflectivity (reflectance) and decorativeness are obtained.

(4) Forming method of colored layer As a forming method of the colored layer, there are a method of pasting a polymer sheet containing a pigment on a polyester film, a method of co-extruding a colored layer at the time of forming a polyester film, a method by coating, and the like. Among these, the method by coating is preferable in that it can be formed with a simple and highly uniform thin film. As a coating method, for example, a known method such as a gravure coater or a bar coater can be used. The solvent of the coating solution used for coating may be water or an organic solvent such as toluene or methyl ethyl ketone. However, from the viewpoint of environmental burden, it is preferable to use water as a solvent.
A solvent may be used individually by 1 type and may be used in mixture of 2 or more types.

(5) Physical property It is preferable that a colored layer contains a white pigment and is comprised as a white layer (light reflection layer). The light reflectance at 550 nm in the case of the reflective layer is preferably 75% or more. When the reflectance is 75% or more, sunlight that has passed through the solar battery cell and has not been used for power generation can be returned to the cell, and the effect of increasing power generation efficiency is high.

  1-20 micrometers is preferable, as for the thickness of a white layer (light reflection layer), 1-10 micrometers is more preferable, More preferably, it is about 1.5-10 micrometers. When the film thickness is 1 μm or more, necessary decoration and reflectance are easily obtained, and when it is 20 μm or less, the surface shape may be deteriorated.

-Undercoat layer-
An undercoat layer can be provided on the polyester film of the present invention. For example, when a colored layer is provided, the undercoat layer may be provided between the colored layer and the polyester film. The undercoat layer can be formed using a binder, a crosslinking agent, a surfactant, and the like.

  Examples of the binder contained in the undercoat layer include polyester, polyurethane, acrylic resin, and polyolefin. In addition to the binder, an epoxy, isocyanate, melamine, carbodiimide, oxazoline, or other crosslinking agent, anionic or nonionic surfactant, silica or other filler may be added to the undercoat layer.

There are no particular restrictions on the method for coating the undercoat layer and the solvent of the coating solution used.
As a coating method, for example, a gravure coater or a bar coater can be used. The solvent may be water or an organic solvent such as toluene or methyl ethyl ketone. A solvent may be used individually by 1 type and may be used in mixture of 2 or more types.

The application may be applied to the polyester film after biaxial stretching or may be applied to the polyester film after uniaxial stretching. In this case, the film may be further stretched in a direction different from the initial stretching after coating. Furthermore, you may extend | stretch in 2 directions, after apply | coating to the polyester film before extending | stretching.
The thickness of the undercoat layer is preferably 0.05 μm to 2 μm, more preferably about 0.1 μm to 1.5 μm. When the film thickness is 0.05 μm or more, the necessary adhesiveness is easily obtained, and when it is 2 μm or less, the surface shape can be favorably maintained.

-Fluorine resin layer / silicon resin layer-
The polyester film of the present invention is preferably provided with at least one of a fluorine-based resin layer and a silicon-based (Si-based) resin layer. By providing the fluorine-based resin layer or the Si-based resin layer, it is possible to prevent contamination of the polyester surface and improve weather resistance. Specifically, it is preferable to have the fluororesin-based coating layer described in JP2007-35694A, JP2008-28294A, and WO2007 / 063698.
Moreover, it is also preferable to stick together fluorine resin films such as Tedlar (manufactured by DuPont).

  The thicknesses of the fluorine-based resin layer and the Si-based resin layer are each preferably in the range of 1 μm to 50 μm, more preferably in the range of 1 μm to 40 μm, and still more preferably in the range of 1 μm to 10 μm.

-Inorganic layer-
The polyester film of the present invention preferably further has a form in which an inorganic layer is provided. By providing the inorganic layer, it is possible to provide a moisture-proof and gas barrier function to prevent water and gas from entering the polyester. The inorganic layer may be provided on either the front or back side of the polyester film, but from the viewpoint of waterproofing, moisture proofing, etc., the side opposite to the battery-side substrate of the polyester film (the side on which the colored layer or easy-adhesion layer is formed) is opposite. It is suitably provided on the side.

Water vapor permeability of the inorganic layer as the (moisture ^{permeability), 10 0 g / m 2} · d~10 -6 g / m 2 · d , more preferably ^{10 1 g / m 2 · d~10} -5 g / ^m is ² · d, more preferably from ^{10 2 g / m 2 · d~10} -4 g / m 2 · d.
In order to form an inorganic layer having such moisture permeability, the following dry method is suitable.

  As a method of forming a gas barrier inorganic layer (hereinafter also referred to as a gas barrier layer) by a dry method, resistance heating vapor deposition, electron beam vapor deposition, induction heat vapor deposition, and vacuum vapor deposition such as an assist method using plasma or ion beam for these. , Reactive sputtering method, ion beam sputtering method, sputtering method such as ECR (electron cyclotron) sputtering method, physical vapor deposition method such as ion plating method (PVD method), heat, light, plasma, etc. Examples include chemical vapor deposition (CVD). Among these, a vacuum vapor deposition method in which a film is formed by a vapor deposition method under vacuum is preferable.

Here, when the material forming the gas barrier layer is mainly composed of inorganic oxide, inorganic nitride, inorganic oxynitride, inorganic halide, inorganic sulfide, etc., it is the same as the composition of the gas barrier layer to be formed. It is possible to directly volatilize the material and deposit it on a substrate or the like. However, when this method is used, the composition changes during volatilization, and as a result, the formed film does not exhibit uniform characteristics. There is a case. Therefore, 1) As a volatilization source, a material having the same composition as the barrier layer to be formed is used. In the case of inorganic oxide, oxygen gas, in the case of inorganic nitride, nitrogen gas, in the case of inorganic oxynitride, oxygen gas A method of volatilizing a mixed gas of nitrogen gas, halogen gas in the case of inorganic halide, and sulfur gas in the case of inorganic sulfide while being introduced into the system, and 2) inorganic substance group as a volatile source And volatilizing this, oxygen gas in the case of inorganic oxide, nitrogen gas in the case of inorganic nitride, mixed gas of oxygen gas and nitrogen gas in the case of inorganic oxynitride, and inorganic halide In the case of halogen-based gas, in the case of inorganic sulfide, sulfur-based gas is introduced into the system, and the inorganic substance and the introduced gas are reacted and deposited on the surface of the substrate. Use this To form an inorganic group layer, and in the case of inorganic oxide, it is in an oxygen gas atmosphere, in the case of inorganic nitride, in a nitrogen gas atmosphere, in the case of inorganic oxynitride, oxygen gas and nitrogen gas In a mixed gas atmosphere, in the case of an inorganic halide, a method of reacting an introduced gas with an inorganic layer by holding in a halogen-based gas atmosphere, and in the case of an inorganic sulfide, a sulfur-based gas atmosphere, and the like.
Among these, 2) or 3) is more preferably used because it is easy to volatilize from a volatile source. Furthermore, the method 2) is more preferably used because the film quality can be easily controlled. When the barrier layer is an inorganic oxide, the inorganic group is used as a volatilization source, volatilized to form an inorganic group layer, and then left in the air to naturally oxidize the inorganic group. The method is also preferable because it is easy to form.

  It is also preferable to use an aluminum foil as a barrier layer by bonding. The thickness is preferably 1 μm or more and 30 μm or less. When the thickness is 1 μm or more, water hardly penetrates into the polyester film during the lapse of time (thermo) and hardly causes hydrolysis, and when it is 30 μm or less, the thickness of the barrier layer does not become too thick, and the barrier layer The stress does not cause the film to bend.

<Solar cell module>
The solar cell module of the present invention comprises a solar cell element that converts light energy of sunlight into electric energy, a transparent substrate on which sunlight is incident, and the polyester film (back sheet for solar cell) of the present invention described above. It is arranged and arranged between. A space between the substrate and the polyester film can be configured by sealing with a resin (so-called sealing material) such as an ethylene-vinyl acetate copolymer.

  The members other than the solar cell module, the solar cell, and the back sheet are described in detail in, for example, “Photovoltaic power generation system constituent material” (supervised by Eiichi Sugimoto, Kogyo Kenkyukai, published in 2008).

  The transparent substrate only needs to have a light-transmitting property through which sunlight can pass, and can be appropriately selected from base materials that transmit light. From the viewpoint of power generation efficiency, the higher the light transmittance, the better. For such a substrate, for example, a glass substrate, a transparent resin such as an acrylic resin, or the like can be suitably used.

  Solar cell elements include silicon-based materials such as single crystal silicon, polycrystalline silicon, and amorphous silicon, III-V groups such as copper-indium-gallium-selenium, copper-indium-selenium, cadmium-tellurium, gallium-arsenide, and II Various known solar cell elements such as -VI group compound semiconductor systems can be applied.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples unless it exceeds the gist thereof. Unless otherwise specified, “part” is based on mass.

(Examples 1 to 29, Comparative Examples 1 to 7)
<Preparation of polyester film>
-1. Preparation of catalyst solution
First, a commercially available basic aluminum chloride aqueous solution (Al ₂ O ₃ equivalent concentration = 14.6% by mass, chlorine ion = 12.1% by mass, pH = 3.1, basicity = 59%) was adjusted to a space velocity of 2. Then, the solution was passed through an acetic acid type anion exchange resin column to obtain a basic aqueous aluminum acetate solution. The analytical values of the aqueous solution were Al ₂ O ₃ = 12.5% by mass, acetate ion = 17.5% by mass, pH = 3.8, and basicity = 60.5%. Ethylene glycol (EG; the same shall apply hereinafter) is added to and mixed with a basic aluminum acetate aqueous solution so that the volume ratio is 1: 1, and water is replaced and removed at 60 ° C. under reduced pressure. Ethylene glycol of basic aluminum acetate A solution was obtained.
Subsequently, Irganox 1222 (manufactured by Ciba Specialty Chemicals Co., Ltd.) as a phosphorus compound was charged into a flask together with ethylene glycol and heated at a liquid temperature of 160 ° C. for 25 hours with stirring under nitrogen substitution, to give 50 g / l of a phosphorus compound of ethylene. A glycol solution was prepared.
Then, the obtained ethylene glycol solution of basic aluminum acetate and ethylene glycol solution of phosphorus compound were charged into a flask and mixed at a room temperature so that the molar ratio of aluminum atoms to phosphorus atoms was 1: 2, one day. Stirring to obtain a catalyst solution.

-2. Preparation of polyester pellets
(1) Al catalyst PET
A 2 liter stainless steel autoclave with a stirrer is charged with high-purity terephthalic acid and twice its amount of ethylene glycol, and 0.3 mol% of triethylamine is added to the acid component at 250 ° C under a pressure of 0.25 MPa An esterification reaction was carried out while distilling water out of the system to obtain a mixture of bis (2-hydroxyethyl) terephthalate and oligomer having an esterification rate of about 95%. The catalyst solution obtained above was used as a polycondensation catalyst for this mixture, and aluminum atoms and phosphorus atoms were added to 0.014 mol% and 0.028 mol%, respectively, with respect to the acid component in the polyester. Thereafter, the mixture was stirred at 250 ° C. for 10 minutes under a nitrogen atmosphere at normal pressure. Next, while raising the temperature to 280 ° C. over 60 minutes, the pressure of the reaction system was gradually reduced to 13.3 Pa (0.1 Torr), and further melt polymerization (polycondensation reaction) was performed at 280 ° C. and 13.3 Pa. . Subsequent to the release of pressure, the resin under slight pressure was discharged into cold water in a strand form and rapidly cooled. After that, the resin was held in cold water for 20 seconds, and then cut to produce cylinder-shaped polyester pellets.
Next, the polyester pellets obtained by melt polymerization are dried under reduced pressure (13.3 Pa or less, 80 ° C., 12 hours), and then crystallized (13.3 Pa or less, 130 ° C. for 3 hours, and further 13.3 Pa or less. , 160 ° C. for 3 hours). After standing to cool, the obtained polyester pellets are put into a solid-phase polymerization reactor, and the solid-state polymerization reaction is carried out while maintaining the system in the vessel at 13.3 Pa or lower and 220 ° C., and polyester pellets having an IV of 0.73 (Raw materials of Examples 1 to 3 and Comparative Examples 1 and 2) were obtained.
In addition, by appropriately changing the melt polymerization time and temperature, and the temperature and time during solid phase polymerization, the concentrations (AV) of the terminal carboxyl groups of the raw material resins of Examples 4 to 29 and Comparative Examples 3 to 6, Intrinsic viscosity (IV) was adjusted as shown in Table 1 below. IV and AV were measured by the following methods.

(2) Sb-catalyzed PET
After 100 parts of dimethyl terephthalate and 70 parts of ethylene glycol were transesterified according to a conventional method using calcium acetate monohydrate and magnesium acetate tetrahydrate as a transesterification catalyst, trimethyl phosphate was added, The transesterification reaction was substantially terminated. Further, titanium tetrabutoxide and antimony trioxide were added. Thereafter, polycondensation was performed according to a conventional method under high temperature and high vacuum, and polyethylene terephthalate having an intrinsic viscosity (IV) = 0.63 and a terminal carboxyl group concentration (AV) = 23 equivalents / ton (raw material resin of Comparative Example 7). Polyester pellets were obtained. IV and AV were measured by the following methods.

-3. Extrusion molding
As the PET raw material resin, the polyester pellets that have been subjected to solid phase polymerization as described above or the polyester pellets and PET recovered waste are used. The temperature was adjusted, put into a hopper of a single-screw kneading extruder, melted at 280 ° C. and extruded. This melt (hereinafter referred to as “melt”) was passed through a gear pump and a filter (pore diameter: 20 μm), and then extruded from a die to a cooling (chill) roll under the following extrusion conditions. The extruded melt was brought into close contact with the cooling roll using an electrostatic application method.
Polyester pellets having a size of Tg: 76 ° C., average major axis: 3 to 5 mm, average minor axis: 1.5 to 2.5 mm, and average length: 4.0 to 5.0 mm were used. Moreover, as PET collection waste used in Examples 12-29, Tg: 76 degreeC, size 50-600 micrometers in thickness, bulk specific gravity 0.40-0.60, and the waste waste [IV: = 0. 78 to 0.80 (difference in IV value from polyester pellets = 0.02 to 0.05), terminal COOH amount: 14 to 15 eq / ton].

  As shown in FIG. 1, the kneading extruder includes a full flight single screw of φ280 and L / D = 36. The length of each part of the screw of this extruder is raw material supply part: screw compression part: measuring part = 12D: 12D: 12D, and the theoretical maximum discharge amount of discharge amount (Q / N) is 2500 kg / h / rpm. is there. In addition, a pressure gauge is attached to each part of the screw (raw material supply part, screw compression part, measuring part) on the outer wall of the cylinder of the kneading extruder. By scanning the longitudinal direction of the groove, the internal pressure of the groove can be measured. Since the screw is rotating at the time of extrusion, the pressure gauge apparently scans (measures) the screw groove width direction (the shortest distance direction between screw flights). The pressure gauge also has a temperature detection function, and can detect the local heat generation temperature of the wall surface resin.

<Extrusion conditions and adjustment>
(A) Resin temperature and oxygen concentration immediately before charging By preheating the resin immediately before charging, the resin temperature T is adjusted to the temperature shown in Table 1 below ((Tg-30) ° C ≦ T ≦ (Tg + 80) ° C). did. Moreover, the oxygen concentration at the extruder inlet shown in Table 1 below was controlled by vacuum suction and nitrogen purge of the input resin.
(B) Ratio of extrusion discharge amount (Q / N) / theoretical maximum discharge amount By controlling the number of rotations of the screw, the bulk specific gravity of the resin used, the back pressure at the screw outlet, and the resin melt temperature, as shown in Table 1 below, The ratio of the extrusion discharge amount (Q / N) to the theoretical maximum discharge amount was adjusted.
(C) Maximum shear rate in the extruder The shear rate shown in Table 1 was adjusted by controlling the rotational speed of the extruder screw and the resin temperature. The shear rate γ and the maximum shear stress σ can be obtained from the following formulas (1) and (2).
Formula (1): γ = π · D · N / 60h
Formula (2): σ = γ × η = (π · D · N / 60h) × η
σ: Maximum shear stress [Pa]
γ: Shear rate [s ⁻¹ ]
η: Viscosity [Pa · s]
D: Screw diameter [mm]
N: Screw rotation speed [rpm]
h: Flight clearance [mm]
(D) Extruding the melt from the die The discharge amount of the extruder and the slit height of the die were adjusted. The cooling rate of the extruded melt was adjusted to the average cooling rate shown in Table 1 by adjusting the temperature of the cooling cast drum and the temperature and air volume of the cool air blown from the auxiliary cooling device installed facing the cooling cast drum. In addition, said cooling rate is an average cooling rate in the 140 to 230 degreeC area | region of the extruded melt film-like thing.
(E) Melt cooling rate The temperature of the cooling cast drum and the temperature and air volume of the cold air blown from the auxiliary cooling device installed facing the cooling cast drum are adjusted, and the cooling is applied to the melt film. Thus, the cooling rate shown in Table 1 below was adjusted. Furthermore, the fine thickness unevenness shown in Table 1 is imparted to the discharged melt, whereby the adhesion between the melt and the cast roll is improved, the cooling efficiency is improved, and the cooling rate is achieved. In addition, the cooling rate was calculated | required in the area | region from the time of the temperature of the extruded melt film-like material becoming 230 degreeC to 140 degreeC.

-4. Stretching
The unstretched film extruded and solidified on the cooling roll by the above method was successively biaxially stretched by the following method to obtain films having the thicknesses shown in Table 1 below.
<Stretching method>
(A) Longitudinal stretching The unstretched film was passed between two pairs of nip rolls having different peripheral speeds and stretched in the longitudinal direction (conveying direction). The preheating temperature was 95 ° C., the stretching temperature was 95 ° C., the stretching ratio was 3.6 times, and the stretching speed was 3000% / second.
(B) Transverse stretching The longitudinally stretched film was stretched laterally under the following conditions using a tenter.
<Condition>
-Preheating temperature: 110 ° C
-Stretching temperature: 130 ° C
-Stretch ratio: 4.0 times-Stretch speed: 150% / second

-5. Thermal fixation / thermal relaxation
Then, the stretched film after finishing longitudinal stretching and lateral stretching was heat-set under the following conditions. Furthermore, after heat setting, the tenter width was reduced and heat relaxation was performed under the following conditions.
<Thermal process conditions>
・ Heat setting temperature: 215 ℃
・ Heat setting time: 3 seconds
<Heat relaxation conditions>
-Thermal relaxation temperature: 210 ° C
-Thermal relaxation rate: 4%

-6. Winding-
After heat setting and heat relaxation, both ends were trimmed by 10 cm. Then, after extruding (knurling) with a width of 10 mm at both ends, it was wound up with a tension of 25 kg / m. The width was 4.8 m and the winding length was 2000 m.
As described above, the PET film for comparison with the present invention (hereinafter referred to as sample film) was produced.

-7. Evaluation of film
About each sample film (PET film) produced as mentioned above, thickness and thickness unevenness, IV, amount of terminal COOH (AV), breaking elongation retention time, foreign matter, withstand voltage were measured and evaluated by the following methods. did. The measurement results are shown in Table 1 below.

(IV value)
IV was determined from the solution viscosity at 30 ° C. in a 1,1,2,2-tetrachloroethane / phenol (= 2/3 [mass ratio]) mixed solvent.

(Terminal COOH amount)
The sample film polyester is completely dissolved in a mixed solution of benzyl alcohol / chloroform (= 2/3; volume ratio), phenol red is used as an indicator, and this is titrated with a standard solution (0.025N KOH-methanol mixed solution). The terminal carboxylic acid group amount (eq / t (equivalent / ton); = terminal COOH amount) was calculated from the appropriate amount.

(Elongation at break elongation = hydrolysis resistance =)
Each sample film was subjected to a thermo treatment at 10 ° intervals in a range of 10 to 300 hours [hr] at 120 ° C. and 100% RH, and then the breaking elongation of each sample after the thermo treatment and before the thermo treatment. Measure the elongation at break for each sample, and based on the measured values, divide the elongation after break by thermo-treatment by the elongation before break, and maintain the break elongation at each thermo-treatment time. The rate was calculated from the following formula. Plotting with the thermo-axis on the horizontal axis and the breaking elongation retention on the vertical axis, the time for heat treatment until the breaking elongation retention reaches 50% (hr; breaking elongation retention half-life) Asked.
The elongation at break (%) was obtained by cutting a sample piece having a size of 1 cm × 20 cm from the polyester film and pulling the sample piece at a rate of 5 cm between chucks and 20% / min.
Break elongation retention half-life indicates that the longer the time, the better the hydrolysis resistance of the polyester film, and it is practically acceptable as hydrolysis resistance to maintain the elongation at break of 50% or more. is there.
Breaking elongation retention [%] = (breaking elongation after thermo treatment) / (breaking elongation before thermo treatment) × 100

(Foreign matter)
For the biaxially stretched sample film thus formed, after detecting foreign matter in the film using a CCD camera or a base surface projector (inspected by changing the angle with reflected light and transmitted light), an enlarged image is taken. The foreign matter was observed using an image processing apparatus and evaluated according to the following evaluation criteria.
<Evaluation criteria>
(Double-circle): Generation | occurrence | production of the foreign material was not seen at all.
○: Slight foreign matter was observed, but was practically acceptable.
Δ: Foreign matter was observed.
X: Generation | occurrence | production of the foreign material was remarkable.

(Thickness unevenness)
Sampling was performed at a width of 35 mm over the entire width of the sample film (TD sample). Moreover, the center part of the width direction was sampled over 2 m length by 35 mm width along the film longitudinal direction (MD sample). TD sample and MD sample were measured with a continuous thickness meter (FILM THICKNESS TESTER KG601A, ANRITSU (manufactured by Anritsu Electric Co., Ltd.)), and the average of (maximum value−average value) and (average value−minimum value) was the thickness unevenness variation value. The thickness unevenness shown in Table 1 below was obtained from the following formula.
Thickness unevenness [%] = Thickness unevenness variation value / average thickness value × 100

(Withstand voltage characteristics)
Each sample film is subjected to a thermo treatment at 120 ° C. and 100% RH for 100 hours, and the sample film before and after the thermo treatment is used and conforms to the plate electrode method in the DC test described in JIS standard C2151. Then, using ITS-6003 (manufactured by Tokyo Seiden Co., Ltd.), the voltage at the time of breakdown (dielectric breakdown voltage) was measured at a pressure increase rate of 0.1 kV / sec. Measurement was performed at n = 50, and the average value was taken as a withstand voltage value. The measurement was performed at room temperature of 25 ° C.
Voltage holding ratio before and after thermo [%] = (withstand voltage after thermo treatment) / (withstand voltage before thermo treatment) × 100

<Preparation of back sheet>
The following (i) reflective layer and (ii) easy-adhesion layer were coated in this order on one side of each sample film obtained above.

(I) Reflective layer (colored layer)
First, various components having the following composition were mixed, and a pigment dispersion was prepared by dispersing for 1 hour using a dynomill type disperser.
<Prescription of pigment dispersion>
・ Titanium dioxide: 39.9 parts (Taipeke R-780-2, manufactured by Ishihara Sangyo Co., Ltd., solid content: 100%)
・ Polyvinyl alcohol: 8.0 parts (PVA-105, manufactured by Kuraray Co., Ltd., solid content: 10%)
・ Surfactant (Demol EP, manufactured by Kao Corporation, solid content: 25%) 0.5 part ・ Distilled water 51.6 parts

Next, using the obtained pigment dispersion, various components having the following composition were mixed to prepare a coating solution for forming a reflective layer.
<Prescription of reflection layer forming coating solution>
・ Pigment dispersion: 80 parts ・ Polyacrylic resin aqueous dispersion: 19.2 parts (Binder: Jurimer ET410, manufactured by Nippon Pure Chemical Industries, Ltd., solid content: 30% by mass) ・ Polyoxy Alkylene alkyl ether: 3.0 parts (Naroacty CL95, manufactured by Sanyo Chemical Industries, solid content: 1% by mass)
Oxazoline compound (crosslinking agent) 2.0 parts (Epocross WS-700, manufactured by Nippon Shokubai Co., Ltd., solid content: 25% by mass)
・ Distilled water: 7.8 parts

The reflective layer-forming coating solution obtained above is applied to a sample film with a bar coater and dried at 180 ° C. for 1 minute to form a reflective layer (white layer) with a titanium dioxide coating amount of 6.5 g / m ^2. did.

(Ii) Easy-adhesive layer Various components having the following composition were mixed to prepare an easy-adhesive layer coating solution, which was applied onto the reflective layer so that the binder coating amount was 0.09 g / m ² . . Then, it was made to dry at 180 degreeC for 1 minute, and the easily bonding layer was formed.
<Composition of coating solution for easy adhesion layer>
・ Polyolefin resin aqueous dispersion: 5.2 parts (Binder: Chemipearl S75N, manufactured by Mitsui Chemicals, solid content: 24% by mass)
Polyoxyalkylene alkyl ether 7.8 parts (Naroacty CL95, manufactured by Sanyo Chemical Industries, solid content: 1% by mass)
・ Oxazoline compound: 0.8 parts (Epocross WS-700, manufactured by Nippon Shokubai Co., Ltd., solid content: 25% by mass)
Silica fine particle aqueous dispersion 2.9 parts (Aerosil OX-50, manufactured by Nippon Aerosil Co., Ltd., solid content: 10% by mass)
・ Distilled water ... 83.3 parts

Next, the following (iii) undercoat layer, (iv) barrier layer, and (v) antifouling layer are provided on the surface of the sample film opposite to the side where the reflective layer and the easily adhesive layer are formed. Coated sequentially from the side.

(Iii) Undercoat layer Various components having the following composition are mixed to prepare a coating solution for an undercoat layer, this coating solution is applied to a sample film, dried at 180 ° C. for 1 minute, and an undercoat layer (dry coating amount: about 0.1 g / m ² ) was formed.
<Composition of coating solution for undercoat layer>
・ Polyester resin: 1.7 parts (Vaironal MD-1200, manufactured by Toyobo Co., Ltd., solid content: 17% by mass)
-Polyester resin ... 3.8 parts (Pesresin A-520, manufactured by Takamatsu Yushi Co., Ltd., solid content: 30% by mass)
Polyoxyalkylene alkyl ether: 1.5 parts (Naroacty CL95, manufactured by Sanyo Chemical Industries, solid content: 1% by mass)
Carbodiimide compound: 1.3 parts (Carbodilite V-02-L2, manufactured by Nisshinbo Co., Ltd., solid content: 10% by mass)
・ Distilled water ... 91.7 parts

(Iv) Barrier layer Subsequently, a vapor deposition film of silicon oxide having a thickness of 800 mm was formed on the surface of the formed undercoat layer under the following vapor deposition conditions to obtain a barrier layer.
<Deposition conditions>
Reaction gas mixture ratio (unit: slm): hexamethyldisiloxane / oxygen gas / helium = 1/10/10
・ Vacuum degree in the vacuum chamber: 5.0 × 10 ⁻⁶ mbar
・ Vacuum degree in the deposition chamber: 6.0 × 10 ⁻² mbar
・ Cooling ・ Electrode drum power supply: 20kW
-Film transport speed: 80 m / min

(V) Antifouling Layer As shown below, a coating solution for forming the first and second antifouling layers is prepared, and the first antifouling layer coating solution and the second antifouling layer are formed on the barrier layer. The coating solution was applied in the order, and a two-layer antifouling layer was applied.

[First antifouling layer]
-Preparation of coating solution for first antifouling layer-
Components in the following composition were mixed to prepare a first antifouling layer coating solution.
<Composition of coating solution>
・ Ceranate WSA1070 (manufactured by DIC Corporation) 45.9 parts
Oxazoline compound (crosslinking agent) 7.7 parts (Epocross WS-700, manufactured by Nippon Shokubai Co., Ltd., solid content: 25% by mass)
・ Polyoxyalkylene alkyl ether: 2.0 parts (Naroacty CL95, manufactured by Sanyo Chemical Industries, solid content: 1% by mass)
・ Pigment dispersion used in the reflective layer: 33.0 parts ・ Distilled water: 11.4 parts

-Formation of first antifouling layer-
The obtained coating solution was coated on the barrier layer so that the binder coating amount was 3.0 g / m ² and dried at 180 ° C. for 1 minute to form a first antifouling layer.

[Second antifouling layer]
-Preparation of coating solution for second antifouling layer-
Components in the following composition were mixed to prepare a second antifouling layer coating solution.
<Composition of coating solution>
Fluorine-based binder: Obligard (manufactured by AGC Co-Tech Co., Ltd.) 45.9 parts Oxazoline compound 7.7 parts (Epocross WS-700, manufactured by Nippon Shokubai Co., Ltd., solid content: 25 mass) %: Crosslinker)
・ Polyoxyalkylene alkyl ether: 2.0 parts (Naroacty CL95, manufactured by Sanyo Chemical Industries, solid content: 1% by mass)
-The pigment dispersion prepared for the reflective layer ... 33.0 parts-Distilled water ... 11.4 parts

-Formation of second antifouling layer-
The prepared coating solution for the second antifouling layer was applied on the first antifouling layer formed on the barrier layer so that the binder application amount was 2.0 g / m ² , and the mixture was applied at 180 ° C. for 1 minute. A second antifouling layer was formed by drying.

  As described above, a back sheet having a reflective layer and an easy adhesion layer on one side of the polyester film and having an undercoat layer, a barrier layer, and an antifouling layer on the other side was produced.

-Evaluation of back sheet-
The backsheet provided with each layer was subjected to a thermo treatment (120 ° C., 100% RH for 100 hours), and then the adhesion was evaluated by the following method. The evaluation results are shown in Table 1 below. Thermo conditions are extremely severe compared to 85 ° C. and 85% RH.

(Adhesion)
In order to evaluate the adhesion force under more severe conditions, the surface (front side) of the sample film constituting the back sheet on which the white layer and the easily adhesive layer are coated, and the back side (the undercoat layer of the sample film, The surface (back surface) on the side where the barrier layer and the antifouling layer are coated) is cut into a grid pattern of 10 pieces at intervals of 5 mm each, and adhesive tape (Nitto Denko Corporation) is applied to each surface. A polyester pressure-sensitive adhesive tape (No. 31B) made was attached and rubbed well for 2 hours in order to familiarize the pressure-sensitive adhesive with the scratches on the grid. Thereafter, the number of grids peeled off at a stretch was counted, the degree of adhesion was calculated from the following formula, and used as an index for evaluating the adhesion.
Adhesiveness (%) = (Number of peeling points) / (Number of all cross-cuts) × 100
Table 1 below shows the average value of the adhesion of the front surface and the adhesion of the back surface. The adhesiveness is a practically acceptable range of 20% or less.
<Evaluation criteria>
A: Adhesion was 5% or less.
○: Adhesion exceeded 5% and was 10% or less.
(Triangle | delta): Adhesiveness exceeded 10% and was 20% or less.
X: Adhesion exceeded 20%.

<Production of solar cell module>
Using each of the back sheets produced as described above, a transparent filler (EVA (ethylene-vinyl acetate copolymer; sealant)) so as to have the structure shown in FIG. 2 of JP-A-2009-158952 And a 30 cm square solar cell module was produced. At this time, it stuck so that the easily-adhesive layer of a backsheet might contact the transparent filler which embeds a solar cell element.

As shown in Table 1, in the examples, the time until the elongation at break is reduced by half is long, high hydrolysis resistance is exhibited, and the solar cell elements arranged on the battery side substrate of the solar cell module are sealed. The adhesiveness between the sealing material (resin material) was excellent. Moreover, the withstand voltage was also good. As a result, the polyester film of the present invention can exhibit high durability for a long period of time even in applications where it is kept for a long time under high temperature, high humidity environment or exposure, such as outdoors.
On the other hand, in the comparative example, the elongation at break was likely to be greatly reduced, and the resistance to hydrolysis was greatly inferior. As a result, the adhesion was poor and the voltage resistance could not be maintained well.

  The polyester film of this invention is used suitably for the use of the back surface sheet | seat (sheet | seat arrange | positioned on the opposite side to the sunlight incident side with respect to a solar cell element; what is called a back sheet | seat) which comprises a solar cell module, for example.

DESCRIPTION OF SYMBOLS 1 ... Back sheet 2 ... Sealant 3 ... Solar cell element 5 ... Screw 6 ... Cylinder 7 ... Hopper 8 ... Raw material resin

Claims (11)

A polyester raw material resin containing at least one selected from the group consisting of aluminum and aluminum compounds as a polymerization catalyst and having an intrinsic viscosity of 0.71 to 0.90 is discharged from an extruder (Q / N; Q is a unit time) Per unit of extrusion [kg / hr], N represents the number of revolutions of the screw [rpm]) is 50% to 80% of the theoretical maximum discharge amount, and melt extrusion is performed by an extruder having a screw outer diameter of φ150 mm or more. An extrusion process;
An unstretched film forming step of forming an unstretched film by cooling and solidifying the melt-extruded polyester resin on a cast roll;
A biaxial stretching step of biaxially stretching the formed unstretched film in the machine direction and the transverse direction;
A heat setting step for heat setting a stretched film formed by biaxial stretching;
The manufacturing method of the polyester film which has this.   The said extrusion process is a manufacturing method of the polyester film of Claim 1 which melt-extrudes in the range whose maximum shear stress ((sigma)) which generate | occur | produces inside the said extruder is 1-1000 KPa.   The said extrusion process melt-extrudes by making oxygen concentration in the said extruder into the range of 0-500 ppm, and making the average residence time in the screw compression part and metering part in the said extruder into 30-120 second. The manufacturing method of the polyester film of description.   The amount of the terminal carboxylic acid group of the said polyester raw material resin is 8-25 eq / ton or less, The manufacturing method of the polyester film of any one of Claims 1-3. The polyester raw resin is represented by the following formula: Tg-30 ° C. ≦ Temperature of polyester resin (° C.) ≦ Tg + 80 °
[Tg: Glass transition temperature]
The manufacturing method of the polyester film of any one of Claims 1-4 which adjusts to the temperature range which satisfy | fills, and throws into the said extruder.   In the unstretched film forming step, the polyester resin melt-extruded from the extruder is cooled and solidified at an average cooling rate of 230 ° C./min to 500 ° C./min in a region where the temperature is 140 ° C. to 230 ° C. The manufacturing method of the polyester film of any one of Claims 1-5.   The said polyester raw material resin contains the collection waste of the polyester resin of the range of more than 0 mass% and 10 mass% or less with respect to the total mass, and the intrinsic viscosity of the said collection waste and the intrinsic viscosity of raw material resin other than the said collection waste The method for producing a polyester film according to any one of claims 1 to 6, wherein the difference is 0.01 to 0.2.   The polyester film produced by the manufacturing method of the polyester film of any one of Claims 1-7.   It contains at least one selected from the group consisting of aluminum derived from a polymerization catalyst and an aluminum compound, has an intrinsic viscosity of 0.71 to 0.90, and has been subjected to a wet heat treatment in an atmosphere of a temperature of 120 ° C. and a relative humidity of 100%. The polyester film according to claim 8, wherein the time during which the breaking elongation is 50% of the breaking elongation before the wet heat treatment is 65 to 150 hours.   The solar cell backsheet containing the polyester film of Claim 8 or Claim 9.   The solar cell module provided with the polyester film of Claim 8 or Claim 9.