JP5710140B2 - Polyester film and method for producing the same, solar cell backsheet, and solar cell module - Google Patents

Description

  The present invention relates to a thick polyester film excellent in weather resistance, a method for producing the same, a back sheet for a solar cell, and a solar cell module.

  The solar cell module generally has a structure in which (sealant) / solar cell element / sealant / back sheet is laminated in this order on glass on which sunlight is incident. Conventionally, a polyester film has been used as a back sheet for this solar cell (hereinafter sometimes abbreviated as BS).

  In recent years, BS has been required to have higher withstand voltage characteristics as compared with conventional ones so that a high-voltage current generated by a solar cell is not short-circuited. In particular, recently, a high withstand voltage of about 600 V to 1000 V or more has been required. For this purpose, it is effective to increase the thickness of the BS.

  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 (BS) for a solar cell for a long time, it tends to peel off on the solar cell and is used for a long time. There is a problem that it has poor practical aptitude. 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 BS is pasted, peeling is likely to occur between the BS and a sealing material such as EVA when left in an environment such as outdoors exposed to wind and rain.

  Such a problem of peeling appears prominently when a thick BS is used, and has become apparent when the thickness exceeds 250 μm, particularly when the thickness is 260 μm or more. The thick film itself is known so far, but there is no knowledge about the above-mentioned peeling when it is thick, and the technology to achieve long-term durability so that peeling does not occur is still established. It has not reached.

  Further, in the above solar cell back surface protection sheet formed by laminating a plurality of polyester resin layers, the number of man-hours increases due to thickening by bonding, and there is a risk of peeling, and the sealing of BS and EVA is not necessarily required. It is not possible to avoid peeling that tends to occur between the stoppers.

  The present invention has been made in view of the above, and is excellent in hydrolysis resistance while having a thick film of 260 μm or more, and seals an adherend (for example, a solar cell element disposed on a battery side substrate of a solar cell module). It is an object to provide a polyester film capable of maintaining adhesion with a resin material such as a sealing material over a long period of time, a manufacturing method thereof, a back sheet for solar cells, and a solar cell module having long-term durability. An object is to achieve the object.

Specific means for achieving the above object are as follows.
<1> The heat treatment time (break elongation retention time) in which the thickness is 260 μm or more and 400 μm or less and the elongation at break after heat treatment at 120 ° C. and 100% RH is maintained at 10% or more (break elongation retention time) is 70 hours or more. It is a polyester film which is 200 hours or less.
<2> The polyester film according to <1>, wherein the moisture content is 0.20% or more and 0.30% or less.
<3> The polyester film according to <1> or <2>, wherein the degree of crystal orientation is from 0.120 to 0.133, and the birefringence is from 0.1657 to 0.1690.
<4> The crystal orientation degree distribution is from 0.1% to 10%, and the birefringence distribution is from 0.1% to 10%, according to any one of <1> to <3>. It is a polyester film.
<5> The polyester film according to any one of <1> to <4>, wherein the amount of the terminal carboxylic acid group is 5 eq / t or more and 24 eq / t or less.
<6> The polyester film according to any one of <1> to <5>, wherein the intrinsic viscosity (IV) is 0.61 or more and 0.9 or less.
<7> The polyester film according to any one of <1> to <6>, which is obtained using a titanium compound as a polymerization catalyst and contains a titanium atom of 1 ppm to 30 ppm.
<8> The polyester film according to any one of <1> to <7>, wherein the absorbance at a wavelength of 380 nm is 0.001 or more and 0.1 or less.

<9> Melting a resin containing polyester and discharging the molten resin discharged in a strip shape having a thickness of 2600 μm or more and 6000 μm or less at an average cooling rate of 250 ° C. to 120 ° C. of the molten resin at 5 ° C. / The molten resin cast at a rate of not less than 80 ° C / second and not more than 80 ° C / second is subjected to vibration of 1 Hz to 100 Hz until the temperature of the molten resin before casting reaches the glass transition temperature (Tg). applying a process for producing a polyester film for performing melt film by.
<10> The method for producing a polyester film according to <9>, wherein the amount of unmelted material in the molten resin is 0.001 piece / kg or more and 0.1 piece / kg or less.
<1 1 > A solar cell backsheet (solar cell back surface protective sheet) comprising the polyester film according to any one of <1> to <8>.
The solar cell back sheet is a protective sheet provided to cover the opposite surface (back surface) of the solar cell module on the side on which sunlight is incident.
<1 2 > A solar cell module including a transparent substrate on which sunlight is incident, a solar cell element, and the polyester film according to any one of <1> to <8>.

According to the present invention, while having a thick film of 260 μm or more, it 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 disposed on a battery side substrate of a solar cell module) ) Can be maintained over a long period of time, and a method for producing the polyester film and a solar cell backsheet can be provided. Also,
According to the present invention, a solar cell module having long-term durability can be provided.

It is a schematic sectional drawing which shows the structural example of a solar cell module.

  Hereinafter, the polyester film of the present invention, the production method thereof, and the solar cell backsheet and solar cell module using the same will be described in detail.

<Polyester film>
The polyester film of the present invention has a thickness of 260 μm or more and 400 μm or less, and a heat treatment time (hereinafter referred to as “breakage”) in which the elongation at break after heat treatment at 120 ° C. and 100% RH is maintained at 10% or more. Also referred to as “elongation retention time”) is 70 hours to 200 hours.

  When a film having a thickness of 260 μm or more is formed, the mechanical performance over time is usually inferior due to deterioration of hydrolysis resistance, etc., but in the present invention, the elongation at break at a predetermined condition of the film is low. When the heat treatment time maintained at 10% or more is 70 hours or more and 200 hours or less, the change accompanying hydrolysis at the adhesion interface with the adherend is suppressed during long-term use, and the adhesion state is stably maintained. Can do. As a result, peeling from the adherend is prevented, and high durability performance is exhibited even when it is placed for a long period of time in a high temperature, high humidity environment or exposure, such as outdoors.

The cause of peeling when the film is formed thick is estimated as follows.
First, the water content of the film is high. That is, when the moisture content of the polyester film is high, the polyester film is easily stretched by moisture content. On the other hand, for example, a battery-side substrate (a substrate on which a solar cell element is provided) of a solar cell module, which is an adherend, is usually formed using a glass substrate and is difficult to expand. Thus, due to the dimensional difference between the polyester film and the adherend, tensile stress is generated in the polyester film, which causes peeling. Particularly in the case of a thick film, this stress tends to increase, and film peeling tends to occur.

Secondly, the hydrolysis resistance of the film is likely to decrease. When hydrolysis resistance is lowered, the molecular weight of the polyester is lowered during long-term use. As a result, the brittleness of the polyester film increases and becomes brittle. Polyester molecules at the interface between a polyester film and an adherend (for example, a solar cell module sealing material (especially EVA)) also become low molecular weight and become brittle. Therefore, the molecules are easily cut by the above-described tensile stress. The interface between the kimono and the kimono is broken and the peeling easily proceeds, and this degradation of hydrolysis resistance is accelerated by water entering the polyester film.
The hydrolysis resistance 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.

From the above points, the polyester film of the present invention has a thickness in the range of 260 μm or more and 400 μm or less from the viewpoint of imparting high withstand voltage characteristics within a practical thickness range. The high withstand voltage of 1000 V or more, which is required recently as the withstand voltage characteristics of the polyester film, can be imparted. In addition, a decrease in hydrolysis resistance can be suppressed. When the thickness is less than 260 μm, the withstand voltage is lowered, and conversely, the thickness exceeding 400 μm is not practical.
Among these, the polyester film is preferably thicker, more preferably in the range of 280 μm to 380 μm, and still more preferably in the range of 290 μm to 360 μm.

  The said withstand voltage is a value calculated | required by measuring the voltage value which short-circuits according to JIST8010.

In the present invention, the film thickness is increased 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 decreases the dimensional stability and hydrolysis resistance. However, the desired long-term durability cannot be obtained. Therefore, the polyester film of the present invention is configured to have a breaking elongation holding time of 70 hours or more and 200 hours or less. Here, the breaking elongation holding time is a heat treatment time [hr] in which the breaking elongation holding ratio after heat treatment (thermo treatment) at 120 ° C. and 100% RH is held in a range of 10% or more. The elongation at break is determined by the following formula (1).
Breaking elongation retention [%] = (breaking elongation after thermo treatment) / (breaking elongation before thermo treatment) × 100 (1)

  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 obtain the heat treatment time [hr] at which the breaking elongation retention is 10% or more.

  The elongation at break is set for each of the MD direction and the TD 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. This is a value obtained by averaging 50 points obtained by repeating 5 times at 20 cm intervals at each point equally divided in the width direction and measuring the obtained values.

  Also, the difference between the maximum value and the minimum value (absolute value) of the 50-point breaking elongation retention time obtained above 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 breaking elongation retention time of the polyester film of the present invention is preferably from 80 hours to 170 hours, more preferably from 100 hours to 150 hours. When the breaking elongation holding time is less than 70 hours, peeling occurs due to the progress of hydrolysis as described above. Further, when the elongation at break elongation exceeds 200 hours, the film moisture content falls below 0.20%. As a result, the crystal structure develops too much in the film, the elastic modulus is high, and the tensile stress increases and peeling occurs. End up.

Thus, it is presumed that the moisture content in the polyester greatly contributes to the above two causes of peeling. In particular, the reason why the water content tends to increase by increasing the thickness of the film is presumed as follows. That is,
In melt film formation of polyester, melted resin (melt) is extruded from a die and rapidly cooled and solidified to prepare an amorphous film, which is then stretched to form a film. The cast film becomes thick and the cooling rate when the molten resin is cooled on the cooling roll is reduced, producing spherulites. This causes stretching unevenness. When an unstretched film containing spherulites is stretched, the spherulites hinder uniform stretching, resulting in the occurrence of high-orientation and low-orientation areas. Therefore, water easily enters and hydrolysis tends to proceed. The water content increases due to the easy entry of water, and the hydrolysis proceeds accordingly.
In order to reduce the moisture content of the polyester film, it is effective to (1) form oriented crystals, (2) strengthen the orientation of molecules (tie molecules) between oriented crystals, and the like.

  Furthermore, the hydrolysis resistance when the film thickness is 260 μm or more is further improved, and an adherend (especially a sealing material (eg, EVA) for sealing the solar cell element of the battery side substrate of the solar cell module); From the viewpoint of further improving the adhesion between the heat treatment, the heat treatment time during which the elongation at break after heat treatment at 120 ° C. and 100% RH is maintained in the range of 40% to 98% is 70 hours to 200 hours ( Preferably it is 80 hours% or more and 170 hours or less, Furthermore, it is preferable that they are 100 hours or more and 150 hours or less), and the elongation at break after heat processing at 120 degreeC and 100% RH is 70% or more and 96% or less It is particularly preferable that the heat treatment time maintained in the range of 70 to 200 hours (preferably 80 hours% to 170 hours, more preferably 100 hours to 150 hours).

  From the viewpoint of preventing the occurrence of peeling as described above, the moisture content of the polyester film is preferably 0.2% or more and 0.3% or less, more preferably 0.22% or more and 0.29% or less, and still more preferably. It is 0.24% or more and 0.28% or less. If the water content exceeds 0.3%, peeling tends to occur for the same reason as described above. Further, when the water content is less than 0.2%, the polyester becomes too hydrophobic, and the adhesion with the adherend (for example, the sealing material of the solar cell module (especially EVA which is a hydrophilic resin)) decreases, Peeling easily occurs.

  The moisture content is determined by leaving the polyester film in an environment of 25 ° C. and 60% RH for 24 hours, and using a Karl Fischer moisture meter (for example, MKC-210 manufactured by Kyoto Electronics Co., Ltd.) for the polyethylene terephthalate after the polyester film is left standing. Is to be measured. The film is used for measurement by heating to 200 ° C. using a vaporizer (for example, ADP-351 manufactured by Kyoto Electronics Co., Ltd.).

In the present invention, in order to adjust the breaking elongation retention rate or breaking elongation retention time and moisture content of the polyester film to the above ranges, 250 ° C. to 120 ° C. of the molten resin when casting the molten resin on a cooling roll. Examples thereof include a method in which the average cooling rate in the temperature range of 5 ° C. is 5 ° C./second or more and 80 ° C./second or less. When the thickness of the molten resin discharged in a strip shape is 2600 μm or more and 6000 μm or less, the cooling rate tends to decrease remarkably. can do. Details of this method and means for achieving cooling will be described later.
In addition, a cooling rate is a cooling rate of molten resin itself, and points out the cooling rate between 250 degreeC-120 degreeC which has the largest influence on crystal formation.

The polyester film of the present invention preferably has a degree of crystal orientation of 0.120 or more and 0.133 or less. The presence of the crystal orientation in the above range indicates that the formation of spherulites is suppressed. That is, a higher crystal orientation value indicates more spherulites and lower crystal orientation, and a lower crystal orientation value indicates fewer spherulites and higher crystal orientation. Since the spherulites are spherical and do not show orientation, the above range is exceeded. Note that spherulites cause an increase in moisture content due to uneven stretching and poor stretching (reduction in orientation). In addition, when the degree of crystal orientation is in the above range, crystal formation is suppressed and the film is easily stretched. Therefore, molecular orientation is facilitated, and the following birefringence can be obtained.
When the degree of crystal orientation is 0.120 or more, an orientation state in which there are few spherulites and crystals are clogged in a rigid state and moisture is difficult to enter is obtained, and the moisture content is kept low. Conversely, if the degree of crystal orientation is 0.133 or less, the crystal structure develops too much in the film and the elastic modulus does not become too high, so the increase in tensile stress is suppressed and the occurrence of peeling is more effectively suppressed. Is done.
Among these, the degree of crystal orientation is more preferably from 0.124 to 0.132, and still more preferably from 0.127 to 0.131.

The crystal orientation distribution is preferably 0.1% or more and 10% or less. By suppressing the generation of spherulites by the above method, the crystal orientation distribution can be set in the above range. As a result, stretching unevenness is suppressed and the moisture content is reduced. That is, when the crystal orientation distribution is suppressed to 10% or less, stretching unevenness is avoided and an increase in moisture content is suppressed. Conversely, when the degree of crystal orientation is 0.1% or more, fluctuations in crystal concentration are formed, and the water content is suppressed. That is, since the oriented crystal is generated by this fluctuation, the degree of orientation is maintained, the increase in the moisture content is suppressed, and the weather resistance can be ensured.
The crystal orientation distribution is more preferably 0.2% or more and 8% or less, and further preferably 0.4% or more and 5% or less.

The degree of crystal orientation is obtained from the following formula by XD measurement of a polyester film.
Degree of crystal orientation = {peak intensity at 2θ = 23 ° ((110) plane)} / {peak intensity at 2θ = 25.8 ° ((100) plane)}

  The birefringence of the polyester film is preferably from 0.1657 to 0.1690, more preferably from 0.1659 to 0.1680, and still more preferably from 0.1661 to 0.1670. If the degree of crystal orientation is in the above range, the formation of crystals is suppressed and the film is easily stretched, so that the molecular orientation is facilitated. Thus, the birefringent biaxially stretched polyester film can be prepared.

The birefringence distribution is preferably in the range of 0.1% to 10%, more preferably 0.2% to 8%, and still more preferably 0.4% to 5%.
In the present invention, a biaxially stretched polyester film having the distribution of crystal orientation and the birefringence distribution is preferable.

The crystal orientation distribution and the birefringence distribution are determined by the following formula.
Crystal orientation degree distribution [%] = (Absolute value of difference between maximum value and minimum value of crystal orientation degree measured at points equally divided in width direction) / (Crystal orientation degree measured at each point equally divided in width direction 10) Average value) x 100
Birefringence distribution [%] = (absolute value of difference between maximum and minimum values of birefringence measured at each point equally divided into 10 in the width direction) / (average of birefringence measured at each point equally divided into 10 in the width direction) Value) x 100
In addition, birefringence is calculated | required from a following formula.
Birefringence = (nx + ny) / 2−nz
[Nx: refractive index in MD direction (width direction: Transverse Direction), ny: birefringence in TD direction (longitudinal direction: Machine Direction), nz: birefringence in thickness direction]

In the polyester film of the present invention, the amount of terminal carboxylic acid group (hereinafter also referred to as “terminal COOH”) (terminal COOH amount; AV) is preferably 5 eq / t or more and 24 eq / t or less. The terminal carboxylic acid has a strong interaction between molecules and promotes the formation of spherulites because the molecules are assembled. For this reason, when the amount of terminal COOH is 24 eq / t or less, the formation of spherulites can be suppressed, and the hydrophilicity of the polyester can be further reduced to reduce the water content. Further, when the amount of terminal COOH is 5 eq / t or more, oriented crystals are generated.
Adjustment to AV as described above can be performed by increasing the degree of vacuum during polymerization and suppressing oxidation due to residual oxygen. It is also preferable to perform solid phase polymerization.

  The amount of terminal COOH is more preferably 7 eq / t or more and 22 eq / t or less, and still more preferably 10 eq / t or more and 20 eq / t or less.

  The terminal COOH amount was determined by dissolving polyester completely in a mixed solution of benzyl alcohol / chloroform (= 2/3; volume ratio), using phenol red as an indicator, and using this as a reference solution (0.025N KOH-methanol mixed solution). ) And calculated from the titration amount.

The intrinsic viscosity (IV: Intrinsic Viscosity) of the polyester film is preferably 0.61 or more and 0.9 or less. 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. In addition, when the value of IV is within the above range, stretchability is good and 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, still more preferably from 0.75 to 0.82.

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]).

The absorbance of the polyester film at 380 nm is preferably from 0.001 to 0.1. When the absorbance is within the above range, it is possible to suppress the polyester film from photodegrading to produce terminal COOH and thus promoting hydrolysis when used as a solar cell backsheet. The absorbance is more preferably from 0.01 to 0.09, still more preferably from 0.02 to 0.08.
The absorbance can be adjusted by adding an organic or inorganic ultraviolet (UV) absorber, but from the viewpoint of maintaining resistance over a long period of time, an inorganic UV absorber may be used. preferable. Examples of the UV absorber include those similar to the ultraviolet absorber described in the section of additive described later. Among these, TiO ₂ is more preferable as the UV absorber. The preferable addition amount of the UV absorber is 0.01% by mass or more and 5% by mass or less, more preferably 0.1% by mass or more and 3% by mass or less, and further preferably 0.3% by mass with respect to the polyester. 3 mass% or less.

  The absorbance is determined by measuring the absorbance at a wavelength of 380 nm with a 300 μm thick polyester film attached to the sample side of the spectrophotometer and the reference side as air.

The polyester film of the present invention is preferably obtained using a titanium compound as a catalyst. Since the titanium compound requires a smaller amount of catalyst than other catalysts (Sb, Ge, Al) other than the titanium compound, the generation of spherulites with the catalyst as a nucleus can be suppressed. The details of the titanium compound will be described in detail in the section of the polyester film production method described later.
When the polyester film is obtained using a titanium compound, titanium atoms are preferably contained in the film in the range of 1 ppm to 30 ppm.

  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.

<Production method of polyester film>
In the method for producing a polyester film of the present invention, a resin containing polyester is melted, and the molten resin discharged in a strip shape having a thickness of 2600 μm or more and 6000 μm or less is placed on a cooling roll (chill roll) at 250 ° C. to 120 ° C. Cast at an average cooling rate at 5 ° C./second or more and 80 ° C./second or less until the molten resin temperature before casting reaches the glass transition temperature (Tg). It is configured to perform melt film formation by applying vibration of 1 Hz to 100 Hz between them.

  The manufacturing method of the polyester film of this invention may be further provided with the esterification process which performs the esterification reaction and / or transesterification reaction for synthesize | combining polyester. Further, a solid phase polymerization step for solid phase polymerization of the polyester to be used may be provided before the polyester is melted.

  When the molten resin is thick after cooling and solidifying after melt-kneading, the spherulites are usually generated because the cooling rate is reduced in the cooling, particularly in the temperature region where crystals are formed. Drawing failure (orientation reduction) occurs. When there is such a low orientation portion, water can easily enter from there, resulting in an increase in the moisture content, which tends to lower the weather resistance. In contrast, in the method for producing a polyester film of the present invention, the average cooling rate of the molten resin in the temperature range of 250 ° C. to 120 ° C. in which crystals are formed even though the thickness of the molten resin to be cooled is as thick as 2600 μm to 6000 μm. Since the molten resin is rapidly cooled on a cooling roll at a temperature of 5 ° C./second or more and 80 ° C./second or less, the production of a spherulite is suppressed, the crystal orientation is large, and a polyester film having a rigid-oriented molecular structure is produced. it can. Thereby, the polyester film excellent in hydrolysis resistance and excellent in weather resistance during long-term use can be obtained.

(1) In the method for producing a polyester film of the present invention, as described above, when the molten resin is cast on a cooling roll (hereinafter also referred to as a cast roll), the average cooling of the molten resin at 250 ° C. to 120 ° C. The speed is set to 5 ° C./second or more and 80 ° C./second or less. The average cooling rate is an average cooling rate between 250 ° C. and 120 ° C. that has the greatest influence on crystal formation. When the average cooling rate is less than 5 ° C./second, spherulites are generated, the breaking elongation retention time is less than 70 hours, and peeling occurs due to the progress of hydrolysis. On the other hand, if the average cooling rate exceeds 80 ° C./second, the breaking elongation retention time exceeds 200 hours, and the melt rapidly solidifies, so that wrinkles are generated on the cast roll, resulting in uneven drawing. When the breaking elongation retention time exceeds 200 hours, the film moisture content is less than 0.20%. As a result, the crystal structure develops too much in the film, the elastic modulus is high, and the tensile stress increases, resulting in peeling. .

Among these, the average cooling rate is preferably 8 ° C./min to 60 ° C./sec, more preferably 10 ° C./min to 40 ° C./sec. Casting at an average cooling rate within the above range can be performed, for example, by the following method.
(A) Method of forcibly supplying air onto the cast roll to cool the molten resin Immediately after landing on the touch roll that is in pressure contact with the cast roll, high-speed cold air is applied to the cast roll (for example, with an air knife) to melt the molten resin (melt )
(B) Method of cooling by touch roll The touch roll is cooled together with the cast roll, and the melt resin (melt) is sandwiched between the touch roll and the cast roll and cooled from both sides of the melt.
(C) Method of water-cooling the melt on the cast roll The melt on the cast roll is rapidly cooled by spraying cold water and / or immersing it in a cold water tank.
Among the above (a) to (c), (b) and (c) are preferable. (B) may be combined with (a) or (c), and (c) may be combined with (a) or (b).

  The average cooling rate is measured with a non-contact thermometer in 10 cm increments from the point where the molten resin (melt) extruded from the die contacts the cast roll. The time for passing the 10 cm interval from the peripheral speed of the cast roll is obtained. Subsequently, this time is taken on the horizontal axis, and the above temperature is plotted on the vertical axis, and the average cooling rate is determined from the average slope of the melt temperature between 250 ° C. and 120 ° C.

  The temperature of the cooling roll itself is preferably 10 ° C. or higher and 80 ° C. or lower, more preferably 15 ° C. or higher and 70 ° C. or lower, and further preferably 20 ° C. or higher and 60 ° C. or lower. Further, from the viewpoint of improving the adhesion between the molten resin (melt) and the cooling roll and increasing the cooling efficiency, it is preferable to apply static electricity before the melt contacts the cooling roll.

  The humidity is 5% RH to 60% RH, more preferably 10% RH to 55%, after the molten resin (melt) is discharged (for example, extruded from the die) until it is brought into contact with the cast roll (air gap). It is preferable to adjust to RH or less, more preferably 15% RH to 50% RH. By adjusting the air hydrophobicity by adjusting the humidity in the air gap to the above range, the penetration of COOH groups and OH groups from the film surface can be adjusted.

When discharging molten resin (melt) (for example, extruding from a die), it is preferable to adjust the shear rate during discharge to a desired range. The shear rate during extrusion is preferably from 1 s ^{−1 to} 300 s ⁻¹ , more preferably from 10 s ^{−1 to} 200 s ⁻¹ , and even more preferably from 30 s ^{−1 to} 150 s ⁻¹ . As a result, for example, die swell (a phenomenon in which the melt expands in the thickness direction) occurs when extruded from a die. That is, since a stress acts in the thickness direction (film normal direction), molecular motion in the melt thickness direction is promoted, and COOH groups and OH groups can be present. When the shear rate is 1 s ⁻¹ or more, COOH groups or OH groups can be sufficiently embedded in the melt, and when it is 300 s ⁻¹ or less, the amount of COOH and OH groups are present on the film surface. be able to.

The thickness of the molten resin (melt) discharged in a band after solidification (before stretching) is in the range of 2600 μm or more and 6000 μm or less, so that a polyester film having a thickness of 260 μm or more and 400 μm or less can be obtained through subsequent stretching. it can. 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 before extending | stretching after solidification is 2600 micrometers or more. Furthermore, the stress at the time of expansion | extension accompanying water content increases, and it is easy to peel off.
Furthermore, when the thickness is 3100 μm or more, it is effective for casting as the above range so that the average cooling rate does not become too fast. As a result, oriented crystals having spherulites as nuclei can be generated, and the weather resistance can be further improved. When the thickness is 6000 μm or less, the cooling rate can be maintained at a level that does not become too slow, and the formation of spherulites is suppressed. As a result, stretching unevenness hardly occurs. Furthermore, although the stretching exotherm increases as the thickness increases, the increase in the moisture content is suppressed because it is difficult to cause a decrease in orientation, and good weather resistance is obtained.

(2) The unmelted material in the molten resin (melt) is preferably 0.001 piece / kg or more and 0.1 piece / kg or less. Spherulites are easily formed using unmelted materials in the melt as nuclei, and formation of spherulites can be suppressed by setting the amount of unmelted materials in the above range. In other words, when the amount of unmelted material is 0.001 piece / kg or more, formation of oriented crystals proceeds well, and when it is 0.1 piece / kg or less, spherulite formation is suppressed. Thus, the crystal orientation is large, and the occurrence of stretching unevenness during stretching is further suppressed.
Note that the unmelted material is a foreign material such as a crystalline material or a decomposed insoluble material, and this foreign material 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 0.1 / kg or more and 0.0. It is 05 pieces / kg or less.

The amount of the unmelted material can be adjusted within the above range by, for example, the following method.
The screw shear rate in the extruder is 50 to 500 sec ⁻¹ (preferably 80 to 400 sec ⁻¹ , more preferably 100 to 350 sec ⁻¹ ). Shear rate, if it is 50 sec ^-1 or more, likely to occur is not yet melt without resin melt and is 500 sec ^-1 or less, the resin in the shear heat generation tends to non melt by thermal decomposition.
In addition, a shear rate is calculated | required by a following formula.
Shear rate [sec ⁻¹ ] = (π × D × N) / (60 × h)
[Π: Circumference ratio, D: Screw diameter (mm), N: Screw rotation speed (rpm), h: Clearance (gap between barrel and screw flight: mm)]

The amount of the unmelted material is determined as follows. That is,
The molten resin (melt) discharged in a band shape (for example, melt extrusion from a die) is rapidly cooled on the cast roll as described above. This is sampled 10 m ² and the number of foreign matters is visually counted on the light table. Divide the number of foreign matters by the mass (kg) of the sample to obtain the number of unmelted materials.

The amount of fine powder in the raw material is preferably 0.01% by mass or more and 5% by mass or less. Furthermore, the amount of the fine powder is more preferably 0.05% by mass or more and 4% by mass or less, and further preferably 0.1% by mass or more and 3% by mass or less. When the amount of the fine powder is 0.01 g or more, the crystal orientation is large when the polyester pellets are dried and melted in the film forming process. Therefore, it is difficult to melt in the gaps between the pellets and it is difficult to melt, so that it tends to be an unmelted product.
The amount of the fine powder can be determined by a method such as washing the pellet with water before drying, removing it with a cyclone, or adding crushed pellets.

(3) between the temperature of the cast before molten resin to reach the glass transition temperature (Tg), to provide a vibration of 1Hz or below 100Hz cast before the molten resin. If this vibration is 1 Hz or more, a suppressing effect is exhibited, and if it is 100 Hz or less, the occurrence of unevenness in the molten resin (melt) is avoided, and the occurrence of stretching unevenness is further suppressed. Such vibration can be applied by applying a rotating body to a die or the like of the film forming apparatus.
The vibration is more preferably given at 5 Hz or more and 90 Hz or less, more preferably 10 Hz or more and 80 Hz or less. Thereby, the production | generation of a spherulite can be suppressed more.

  The above (1) to (3) may be performed independently, but a synergistic effect can be obtained by combining them. Thereby, even if it is a single layer (even if it does not laminate | stack with another raw material) or a single material (even if it does not blend), high weather resistance is acquired.

The area stretch ratio (longitudinal stretch ratio × transverse stretch ratio) after solidification after casting (before stretching) is preferably 10 to 18 times, more preferably 12 to 16 times, and even more preferably 12.5. It is not less than 15 times and not more than 15. The ratio between the longitudinal draw ratio and the transverse draw ratio (longitudinal draw ratio / lateral draw ratio) is preferably 0.7 or more and 1.3 or less, more preferably 0.75 or more and 1.0 or less, and still more preferably 0.8. It is 0.95 or less.
At this time, in the present invention, the thickness after stretching is preferably 260 μm or more and 400 μm or less, and the thickness after stretching is preferably 280 μm or more and 380 μm or less, more preferably 290 μm or more and 360 μm or less.
When the thickness after stretching exceeds 400 μm, the elasticity becomes too strong, which is caused by the difference in the amount of expansion and contraction with the adherend (especially the sealing material (particularly EVA) provided on the battery side substrate of the solar cell module). Elongation and shrinkage stress increase and peeling easily occurs. Further, if the thickness after stretching is less than 260 μm, the elasticity of the film is small, so that warping due to the difference in stretch and shrinkage with the adherend (especially sealing material such as EVA) is likely to occur. The accompanying peeling occurs.

-Esterification process-
In this invention, the esterification process which provides an esterification reaction and a polycondensation reaction and produces | generates polyester can be provided. 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.

(A) Esterification reaction In the esterification reaction at the time of polymerizing polyester, a titanium (Ti) compound, an antimony compound, a germanium compound, an aluminum compound, or the like can be used as a catalyst. Details of the catalyst will be described later. Among these, it is preferable to use a Ti compound as a catalyst. In this case, the addition amount of the Ti compound is preferably 1 ppm or more and 30 ppm or less in terms of Ti element, more preferably 2 ppm or more and 20 ppm or less, and further preferably 3 ppm or more and 15 ppm or less.
When the amount of the Ti-based compound is 1 ppm or more in terms of Ti element, the polymerization rate is increased and preferable IV is obtained. If the amount of Ti compound is 30 ppm or less in terms of Ti element, the amount of terminal COOH can be adjusted to satisfy the above range, and a good color tone can be obtained.

  For the synthesis of Ti-based polyester using such a Ti compound, for example, Japanese Patent Publication No. 8-30119, Japanese Patent No. 2543624, Japanese Patent No. 3335683, Japanese Patent No. 3717380, Japanese Patent No. 397756, and Japanese Patent No. 396226 are disclosed. Japanese Patent No. 3997866, Japanese Patent No. 3996687, Japanese Patent No. 40000867, Japanese Patent No. 4053837, Japanese Patent No. 4127119, Japanese Patent No. 4134710, Japanese Patent No. 4159154, Japanese Patent No. 4269538, Japanese Patent No. The methods described in JP 2005-340616 A, JP 2005-239940 A, JP 2004-319444 A, JP 2007-204538 A, Japanese Patent No. 3436268, Japanese Patent No. 3780137, and the like can be applied.

  Polyesters forming the polyester film of the present invention are (A) malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecanedioic acid, dimer acid, eicosandioic acid, pimelic acid, azelaic acid, Aliphatic dicarboxylic acids such as methyl malonic acid and ethyl malonic acid, adamantane dicarboxylic acid, norbornene dicarboxylic acid, isosorbide, cyclohexane dicarboxylic acid, decalin dicarboxylic acid, terephthalic acid, isophthalic acid, phthalic acid, 1 , 4-Naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 4,4′-diphenyldicarboxylic acid, 4,4′-diphenyletherdicarboxylic acid, 5 -Sodium sulfoi A dicarboxylic acid such as phthalic acid, phenylendanedicarboxylic acid, anthracene dicarboxylic acid, phenanthrene dicarboxylic acid, aromatic dicarboxylic acid such as 9,9′-bis (4-carboxyphenyl) fluorenic acid or an ester derivative thereof; and (B) ethylene glycol. 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-butanediol, aliphatic diols such as 1,3-butanediol, cyclohexanedimethanol, spiroglycol, isosorbide Diols such as aromatic diols such as alicyclic diols such as bisphenol A, 1,3-benzenedimethanol, 1,4-benzenedimethanol, 9,9′-bis (4-hydroxyphenyl) fluorene Esterification of compounds with known methods It can be obtained by response and / or transesterification.

It is preferable that at least one aromatic dicarboxylic acid is used as the dicarboxylic acid component. More preferably, the dicarboxylic acid component contains an aromatic dicarboxylic acid as a main component. The “main component” means that the proportion of aromatic dicarboxylic acid in the dicarboxylic acid component is 80% by mass or more. A dicarboxylic acid component other than the aromatic dicarboxylic acid may be included. Examples of such a dicarboxylic acid component include ester derivatives such as aromatic dicarboxylic acids.
Further, it is preferable that at least one aliphatic diol is used as the diol component. The aliphatic diol can contain ethylene glycol, and preferably contains ethylene glycol as a main component. The main component means that the proportion of ethylene glycol in the diol component is 80% by mass or more.

  The amount of the aliphatic diol (for example, ethylene glycol) used is in the range of 1.015 to 1.50 mol with respect to 1 mol of the aromatic dicarboxylic acid (for example, terephthalic acid) and, if necessary, its ester derivative. Is preferred. The amount used is more preferably in the range of 1.02 to 1.30 mol, and still more preferably in the range of 1.025 to 1.10 mol. If the amount used is in the range of 1.015 or more, the esterification reaction proceeds favorably, and if it is in the range of 1.50 mol or less, for example, by-production of diethylene glycol due to dimerization of ethylene glycol is suppressed, Many characteristics such as melting point, glass transition temperature, crystallinity, heat resistance, hydrolysis resistance, and weather resistance can be kept good.

  PET preferably contains 90% by mole or more of terephthalic acid and ethylene glycol, more preferably 95% by mole or more, and still more preferably 98% by mole or more.

  Conventionally known reaction catalysts can be used for the esterification reaction and / or the transesterification reaction. Examples of the reaction catalyst include alkali metal compounds, alkaline earth metal compounds, zinc compounds, lead compounds, manganese compounds, cobalt compounds, aluminum compounds, antimony compounds, titanium compounds, germanium compounds, and phosphorus compounds. Usually, it is preferable to add an antimony compound, a germanium compound, or a titanium compound as a polymerization catalyst at an arbitrary stage before the polyester production method is completed. As such a method, for example, when a germanium compound is taken as an example, it is preferable to add the germanium compound powder as it is.

  Among these, more preferable polyesters are polyethylene terephthalate (PET) and polyethylene-2,6-naphthalate (PEN), and still more preferable is PET. The PET is polymerized using one or more selected from a germanium (Ge) -based catalyst, an antimony (Sb) -based catalyst, an aluminum (Al) -based catalyst, and a titanium (Ti) -based catalyst. PET is preferable, and a Ti-based catalyst is more preferably used.

  The Ti-based catalyst has high reaction activity and can lower the polymerization temperature. Therefore, in particular, it is possible to suppress the thermal decomposition of PET during the polymerization reaction and the generation of COOH, which is suitable for adjusting the amount of terminal COOH to a predetermined range in the polyester film of the present invention.

Examples of the Ti-based catalyst include oxides, hydroxides, alkoxides, carboxylates, carbonates, oxalates, organic chelate titanium complexes, and halides. The Ti-based catalyst may be used in combination of two or more titanium compounds as long as the effects of the present invention are not impaired.
Examples of Ti-based catalysts include tetra-n-propyl titanate, tetra-i-propyl titanate, tetra-n-butyl titanate, tetra-n-butyl titanate tetramer, tetra-t-butyl titanate, tetracyclohexyl titanate, tetraphenyl Titanium alkoxide such as titanate and tetrabenzyl titanate, titanium oxide obtained by hydrolysis of titanium alkoxide, titanium-silicon or zirconium composite oxide obtained by hydrolysis of a mixture of titanium alkoxide and silicon alkoxide or zirconium alkoxide, titanium acetate , Titanium oxalate, potassium potassium oxalate, sodium oxalate, potassium titanate, sodium titanate, titanium titanate-aluminum hydroxide mixture, titanium chloride, titanium chloride-aluminum chloride Miniumu mixture, titanium acetylacetonate, an organic chelate titanium complex having an organic acid as a ligand, and the like.

  Among the Ti-based catalysts, at least one of organic chelate titanium complexes having an organic acid as a ligand can be suitably used. Examples of the organic acid include citric acid, lactic acid, trimellitic acid, malic acid and the like. Among them, an organic chelate complex having citric acid or citrate as a ligand is preferable.

For example, when a chelate titanium complex having citric acid as a ligand is used, there is little generation of foreign matters such as fine particles, and a polyester resin having better polymerization activity and color tone than other titanium compounds can be obtained. Furthermore, even when using a citric acid chelate titanium complex, by adding it at the stage of the esterification reaction, a polyester resin having better polymerization activity and color tone and less terminal carboxyl groups can be obtained compared to the case where it is added after the esterification reaction. It is done. In this regard, the titanium catalyst also has a catalytic effect of the esterification reaction. By adding it at the esterification stage, the oligomer acid value at the end of the esterification reaction is lowered, and the subsequent polycondensation reaction is performed more efficiently. In addition, complexes with citric acid as a ligand are more resistant to hydrolysis than titanium alkoxides, etc., and do not hydrolyze in the esterification reaction process, while maintaining the original activity and catalyzing the esterification and polycondensation reactions It is estimated to function effectively as
In general, it is known that the greater the amount of terminal carboxyl groups, the worse the hydrolysis resistance. By reducing the amount of terminal carboxyl groups by the addition method of the present invention, improvement in hydrolysis resistance is expected. The
Examples of the citric acid chelate titanium complex are readily available as commercial products such as VERTEC AC-420 manufactured by Johnson Matthey.

  The aromatic dicarboxylic acid and the aliphatic diol can be introduced by preparing a slurry containing them and continuously supplying it to the esterification reaction step.

  In the present invention, an aromatic dicarboxylic acid and an aliphatic diol are polymerized in the presence of a catalyst containing a titanium compound, and at least one of the titanium compounds is an organic chelate titanium complex having an organic acid as a ligand. It is preferable that an esterification reaction process including at least a process of adding an organic chelate titanium complex, a magnesium compound, and a pentavalent phosphate ester having no aromatic ring as a substituent in this order is provided. In this case, in addition to this esterification reaction step, production of a polyester resin comprising a polycondensation step in which a polycondensation product is produced by polycondensation reaction of the esterification reaction product produced in the esterification reaction step The aspect which produces a polyester film by a method is more preferable. The polycondensation step will be described later.

In this case, in the course of the esterification reaction, the addition of a magnesium compound to the presence of an organic chelate titanium complex as a titanium compound, followed by the addition order of adding a specific pentavalent phosphorus compound, thereby providing a titanium catalyst. As the result, the coloring reaction is less and the electrostatic application property is high. At the same time, a polyester resin with improved yellowing when exposed to high temperatures is obtained.
As a result, coloring during polymerization and subsequent coloring during melt film formation are reduced, and yellowishness is reduced compared to conventional antimony (Sb) catalyst-based polyester resins, and germanium catalysts having a relatively high transparency are also obtained. It is possible to provide a polyester resin having a color tone and transparency comparable to a polyester resin and having excellent heat resistance. Further, a polyester resin having high transparency and less yellowness can be obtained without using a color tone adjusting material such as a cobalt compound or a pigment.

  This polyester resin can be used for applications requiring high transparency (for example, optical film, industrial squirrel, etc.), and it is not necessary to use an expensive germanium-based catalyst, so that the cost can be greatly reduced. In addition, since foreign matters caused by the catalyst that are likely to occur in the Sb catalyst system are also avoided, the occurrence of failures and quality defects in the film forming process can be reduced, and the cost can be reduced by improving the yield.

  In the above, when the aromatic dicarboxylic acid and the aliphatic diol are mixed with a catalyst containing an organic chelate titanium complex that is a titanium compound prior to the addition of the magnesium compound and the phosphorus compound, the organic chelate titanium complex or the like is subjected to an esterification reaction. Therefore, the esterification reaction can be carried out satisfactorily. At this time, you may add a titanium compound in mixing the dicarboxylic acid component and the diol component. Moreover, after mixing a dicarboxylic acid component (or diol component) and a titanium compound, you may mix a diol component (or dicarboxylic acid component). Further, the dicarboxylic acid component, the diol component, and the titanium compound may be mixed at the same time. The mixing is not particularly limited, and can be performed by a conventionally known method.

  In the esterification reaction, it is preferable to provide a process in which an organic chelate titanium complex which is a titanium compound and a magnesium compound and a pentavalent phosphorus compound as additives are added in this order. At this time, the esterification reaction proceeds in the presence of the organic chelate titanium complex, and thereafter, the addition of the magnesium compound is started before the addition of the phosphorus compound.

(Phosphorus compound)
As the pentavalent phosphorus compound, at least one pentavalent phosphate having no aromatic ring as a substituent is used. Examples of the pentavalent phosphate ester in the present invention include trimethyl phosphate, triethyl phosphate, tri-n-butyl phosphate, trioctyl phosphate, tris phosphate (triethylene glycol), methyl acid phosphate, and phosphoric acid. Examples include ethyl acid, isopropyl acid phosphate, butyl acid phosphate, monobutyl phosphate, dibutyl phosphate, dioctyl phosphate, and triethylene glycol acid phosphate.

Among pentavalent phosphates, phosphates having a lower alkyl group having 2 or less carbon atoms as a substituent [(OR) ₃ —P═O; R = an alkyl group having 1 or 2 carbon atoms] are preferable, Specifically, trimethyl phosphate and triethyl phosphate are particularly preferable.

  In particular, when a chelate titanium complex coordinated with citric acid or a salt thereof is used as the catalyst as the titanium compound, the pentavalent phosphate ester has better polymerization activity and color tone than the trivalent phosphate ester. Furthermore, in the case of adding a pentavalent phosphate having 2 or less carbon atoms, the balance of polymerization activity, color tone, and heat resistance can be particularly improved.

  The addition amount of the phosphorus compound is preferably such that the P element conversion value is in the range of 50 ppm to 90 ppm. The amount of the phosphorus compound is more preferably 60 ppm to 80 ppm, and still more preferably 65 ppm to 75 ppm.

(Magnesium compound)
Inclusion of the magnesium compound improves electrostatic applicability. In this case, although it is easy to color, in this invention, coloring is suppressed and the outstanding color tone and heat resistance are obtained.

  Examples of the magnesium compound include magnesium salts such as magnesium oxide, magnesium hydroxide, magnesium alkoxide, magnesium acetate, and magnesium carbonate. Among these, magnesium acetate is most preferable from the viewpoint of solubility in ethylene glycol.

  The amount of magnesium compound added is preferably such that the Mg element conversion value is 50 ppm or more, more preferably 50 ppm or more and 100 ppm or less in order to impart high electrostatic applicability. The addition amount of the magnesium compound is preferably an amount that is in the range of 60 ppm to 90 ppm, more preferably 70 ppm to 80 ppm in terms of imparting electrostatic applicability.

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

  In the present invention, no special synthesis or the like is required, and the titanium compound, phosphorus compound, and magnesium compound, which are inexpensive and easily available, are used for color tone and heat while having the reaction activity required for the reaction. A polyester resin excellent in coloring resistance can be obtained.

  In the formula (ii), from the viewpoint of further enhancing the color tone and the coloration resistance to heat while maintaining the polymerization reactivity, it is preferable to satisfy + 1.0 ≦ Z ≦ + 4.0, and + 1.5 ≦ Z ≦ + 3 Is more preferable.

  As a preferred embodiment in the present invention, before the esterification reaction is completed, after adding a chelate titanium complex having 1 ppm or more and 30 ppm or less of citric acid or citrate as a ligand to the aromatic dicarboxylic acid and the aliphatic diol, In the presence of the chelate titanium complex, a magnesium salt of a weak acid of 60 ppm or more and 90 ppm or less (more preferably 70 ppm or more and 80 ppm or less) is added. And an embodiment in which a pentavalent phosphate having no aromatic ring as a substituent is added.

  The esterification reaction may be carried out using a multistage apparatus in which at least two reactors are connected in series under conditions where ethylene glycol is refluxed while removing water or alcohol produced by the reaction from the system. it can.

The esterification reaction described above may be performed in one stage or may be performed in multiple stages.
When the esterification reaction is performed in one step, the esterification reaction temperature is preferably 230 to 260 ° C, more preferably 240 to 250 ° C.
When the esterification reaction is performed in multiple stages, the temperature of the esterification reaction in the first reaction tank is preferably 230 to 260 ° C, more preferably 240 to 250 ° C, and the pressure is 1.0 to 5.0 kg / cm ² is preferable, and 2.0 to 3.0 kg / cm ² is more preferable. Temperature of the esterification reaction of the second reaction vessel is preferably from 230 to 260 ° C., more preferably from 245 to 255 ° C., the pressure is 0.5~5.0kg / cm ^2, more preferably 1.0 to 3. 0 kg / cm ² . Furthermore, when carrying out by dividing into three or more stages, it is preferable to set the conditions for the esterification reaction in the intermediate stage to the conditions between the first reaction tank and the final reaction tank.

(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.

In the present invention, by providing the esterification reaction step and the polycondensation step described above, the titanium atom (Ti), the magnesium atom (Mg), and the phosphorus atom (P) are included and calculated from the following formula (i). Value Z can produce a polyester resin composition satisfying the following relational expression (ii).
(I) Z = 5 × (P content [ppm] / P atomic weight) −2 × (Mg content [ppm] / Mg atomic weight) −4 × (Ti content [ppm] / Ti atomic weight)
(Ii) + 0 ≦ Z ≦ + 5.0

  The polyester resin composition satisfies + 0 ≦ Z ≦ + 5.0, and the balance of the three elements of Ti, P, and Mg is appropriately adjusted, so that the polymerization reactivity is maintained, It is excellent in color tone and heat resistance (reduction of yellow coloring under high temperature) and can maintain high electrostatic applicability. Moreover, in this invention, it has high transparency, without using color tone adjusting materials, such as a cobalt compound and a pigment | dye, and can obtain polyester resin with little yellowishness.

As described above, the formula (i) is a quantitative expression of the balance between the phosphorus compound, the magnesium compound, and the phosphorus compound, and the phosphorus content acting on the magnesium from the total amount of phosphorus that can be reacted. This represents the amount of phosphorus that can act on titanium. If the value Z is less than +0, that is, if the amount of phosphorus acting on titanium is too small, the catalytic activity (polymerization reactivity) of titanium will increase, but the heat resistance will decrease, and the resulting polyester resin will have a yellowish color and polymerize. For example, it is colored at the time of film formation (melting) later, and the color tone is lowered. On the other hand, if the value Z exceeds +5.0, that is, the amount of phosphorus acting on titanium is too large, the resulting polyester has good heat resistance and color tone, but the catalytic activity is too low and the productivity is poor.
In the present invention, for the same reason as described above, the formula (ii) preferably satisfies 1.0 ≦ Z ≦ 4.0, and more preferably satisfies 1.5 ≦ Z ≦ 3.0.

  Measurement of each element of Ti, Mg, and P is obtained by quantifying each element in PET using high-resolution inductively coupled plasma-mass spectrometry (HR-ICP-MS; AttoM manufactured by SII Nanotechnology). It can carry out by calculating content [ppm] from the obtained result.

Moreover, it is preferable that the produced | generated polyester resin composition satisfy | fills the relationship represented by the following relational expression (iii) further.
B value when pelletized after polycondensation ≦ 4.0 (iii)
When the polyester resin obtained by polycondensation is pelletized and the b value of the pellet is 4.0 or less, yellowness is small and the transparency is excellent. When the b value is 3.0 or less, the color tone is comparable to that of a polyester resin polymerized with a Ge catalyst.

  The b value is an index representing the color and is a value measured using ND-101D (manufactured by Nippon Denshoku Industries Co., Ltd.).

Furthermore, the polyester resin composition preferably satisfies the relationship represented by the following relational expression (iv).
Color tone change rate [Δb / min] ≦ 0.15 (iv)
When the polyester resin pellets obtained by polycondensation are melt-held at 300 ° C., the color change rate [Δb / min] is 0.15 or less, so that yellow coloring when exposed to heating is low. Can be suppressed. Thereby, when extruding with an extruder, for example, to form a film, a film with little yellow coloring and excellent color tone can be obtained.

  The color change rate is preferably as small as possible, and is particularly preferably 0.10 or less.

The color tone change rate is an index representing a color change due to heat, and is a value obtained by the following method. That is,
The pellets of the polyester resin composition are put into a hopper of an injection molding machine (for example, EC100NII manufactured by Toshiba Machine Co., Ltd.) and melted and held in a cylinder (300 ° C.). The plate b value at this time is measured by ND-101D (manufactured by Nippon Denshoku Industries Co., Ltd.). The rate of change [Δb / min] is calculated based on the change in the b value.

-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 solid phase polymerization is performed at 150 ° C. or higher and 250 ° C. or lower, more preferably 170 ° C. or higher and 240 ° C. or lower, more preferably 190 ° C. or higher and 230 ° C. or lower for 5 hours or longer and 100 hours or shorter, more preferably 10 hours or longer and 80 hours or shorter, Preferably, it is carried out under conditions of 15 hours or more and 60 hours or less. In addition, the solid phase polymerization is preferably performed in a vacuum or in a nitrogen (N ₂ ) stream. Furthermore, you may mix polyhydric alcohol (ethylene glycol etc.) 1 ppm or more and 1% or less.

  Solid-phase polymerization may be carried out in a batch mode (a method in which a resin is placed in a container and stirred while applying heat for a predetermined time), or a continuous mode (a resin is placed in a heated cylinder and this is stirred). It may be carried out by a system in which the gas is passed through the cylinder while being kept flowing for a predetermined time while being heated, and sequentially fed out.

-Molding process-
In the forming step, the polyester after the solid phase polymerization step is melt-kneaded and extruded from a die (extrusion die) to form the polyester film described above.

The polyester obtained in the above solid phase polymerization step can be dried to reduce the residual moisture to 100 ppm or less, and then melted using an extruder. The melting temperature is preferably 250 ° C. or higher and 320 ° C. or lower, more preferably 260 ° C. or higher and 310 ° C. or lower, further preferably 270 ° C. or higher and 300 ° C. or lower. The extruder may be uniaxial or multi-axial. More preferably, the inside of the extruder is replaced with nitrogen from the viewpoint that generation of terminal COOH due to thermal decomposition can be further suppressed.
The melted molten resin (melt) is extruded from an extrusion die through a gear pump, a filter or the like. At this time, it may be extruded as a single layer or may be extruded as a multilayer.

-Stretching process-
After the above step, the polyester film of the present invention can be suitably produced by biaxially stretching the produced extruded film (unstretched film).

  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.

<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 400% by mass, 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 Chemical 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.

(Example 1)
-1. Synthesis of polyethylene terephthalate
(1) PET-1: Ti catalyst As shown below, terephthalic acid and ethylene glycol are directly reacted to distill off water, esterify, and then use a direct esterification method in which polycondensation is performed under reduced pressure. A polyester resin (PET sample) was obtained using a continuous polymerization apparatus.

-Esterification reaction-
4.7 tons of high-purity terephthalic acid and 1.8 tons of ethylene glycol were mixed over 90 minutes to form a slurry, and continuously fed to the first esterification reactor at a flow rate of 3800 kg / h. Furthermore, an ethylene glycol solution of a citrate chelate titanium complex (VERTEC AC-420, manufactured by Johnson Matthey) in which citric acid is coordinated to Ti metal was continuously supplied, and the average temperature was 250 ° C. with stirring in the reaction vessel. The reaction was carried out with a residence time of about 4.3 hours. At this time, the citric acid chelate titanium complex was continuously added so that the amount of Ti added was 9 ppm in terms of element. At this time, the acid value of the obtained oligomer was 600 eq / ton.

  This reaction product was transferred to a second esterification reaction vessel and reacted with stirring at a temperature in the reaction vessel of 250 ° C. and an average residence time of 1.2 hours to obtain an oligomer having an acid value of 200 eq / ton. The inside of the second esterification reaction tank is partitioned into three zones. Among the three zones, the ethylene glycol solution of magnesium acetate is continuously added from the second zone so that the added amount of Mg is 75 ppm in terms of element. Subsequently, an ethylene glycol solution of trimethyl phosphate was continuously supplied from the third zone so that the amount of P added was 65 ppm in terms of element.

-Polycondensation reaction-
The obtained esterification reaction product was continuously supplied to the first polycondensation reaction tank, and with stirring, the reaction temperature was 270 ° C., the reaction tank internal pressure was 2.67 × 10 ⁻³ MPa (20 torr), and the average residence time was The polycondensation was performed in about 1.8 hours. Further, the mixture was transferred to the second double condensation reaction tank, and while stirring in this reaction tank, the reaction tank temperature was 276 ° C., the reaction tank pressure was 6.67 × 10 ⁻⁴ MPa (5 torr), and the residence time was about 1.2 hours. The reaction (polycondensation) was performed under the conditions. Subsequently, it was further transferred to the third triple condensation reaction vessel, and in this reaction vessel, the temperature in the reaction vessel was 278 ° C., the pressure in the reaction vessel was 2.0 × 10 ⁻⁴ MPa (1.5 torr), and the residence time was 1.5 hours. The reaction (polycondensation) was carried out to obtain polyethylene terephthalate.

  About the polyethylene terephthalate obtained above, using high resolution high frequency inductively coupled plasma-mass spectrometry (HR-ICP-MS; AttoM manufactured by SII Nanotechnology), titanium element (Ti), magnesium element (Mg) in PET ) And phosphorus element (P) were quantified, and the content [ppm] was calculated from the obtained results. As a result, Ti = 9 ppm, Mg = 75 ppm, and P = 60 ppm. In addition, although P has decreased slightly with respect to the initial addition amount, it is estimated that it volatilized in the polymerization process.

(2) PET-2: Sb catalyst A PET sample was obtained according to the method shown below. That is,
Ethylene glycol (64 parts) was mixed with 100 parts of dimethyl terephthalate, 0.1 parts of zinc acetate and 0.03 part of antimony trioxide were added as catalysts, and transesterification was performed at the reflux temperature of ethylene glycol. To this was added 0.08 part of trimethyl phosphate, the temperature was gradually raised and the pressure was reduced, and a polymerization reaction was carried out at 271 ° C. for 5 hours to obtain polyethylene terephthalate (hereinafter referred to as PET-a). Moreover, the intrinsic viscosity (IV) of the obtained PET-a was 0.55. This PET-a is cut into a chip having a length of 4 mm, and the obtained chip is placed in a rotary vacuum device (rotary vacuum dryer) in which conditions of a temperature of 220 ° C. and a degree of vacuum of 0.5 mmHg are set, and stirred for 20 hours. In addition to the above, polyethylene terephthalate (hereinafter referred to as PET-b) was obtained.

  The obtained PET-a and b were each subjected to vacuum drying at a temperature of 180 ° C., a degree of vacuum of 0.5 mmHg, and a time of 2 hours, and an ultraviolet absorber (tinuvin (registered trademark) P, Ciba A PET sample was prepared by blending 5% by mass of Specialty Chemicals.

(3) PET-3: Ge catalyst According to the method shown below, a PET sample was obtained. That is,
A slurry of high-purity terephthalic acid and ethyl glycol was continuously fed to the first esterification reactor containing the reactants in advance and averaged residence at about 250 ° C. and 0.5 kg / cm ² with stirring. The reaction was carried out for 3 hours. This reaction product was transferred to the second esterification reactor, and the reaction was carried out with stirring at about 260 ° C. and 0.05 kg / cm ² to a predetermined reactivity. In addition, crystalline germanium dioxide is dissolved in water by heating, ethylene glycol is added thereto, and the heat-treated catalyst solution and the ethylene glycol solution of phosphoric acid are separately added continuously to the second esterification reactor. Supplied. The esterification reaction product is continuously fed to the first polymerization reactor, with stirring at about 265 ° C., 25 torr for 1 hour, then with the second polymerization reactor, with stirring at about 265 ° C., 3 torr for 1 hour, Further, polymerization was carried out for 1 hour at about 275 ° C. and 0.5 to 1 torr with stirring in the final polymerization reactor. Thereafter, a linear low density polyethylene (MI = 0.9 g / 10 min, density = 0.923 g / cm ³ ) was added to an average dispersed particle size of 2 μm or less by a mixer installed downstream of the final polycondensation reactor. The dispersed molten PET master was mixed so that the polyethylene content was 50 ppb to obtain a PET chip. The obtained PET had an IV of 0.54 and a DEG content of 2.4 mol%.
The molten PET master (polyethylene content: about 100 ppm) in which polyethylene was finely dispersed was kneaded with dry PET and the polyethylene powder with a twin screw extruder, passed through a 3 μm sintered metal filter, and then pelletized. Is. The average dispersion diameter of polyethylene was 2 μm or less.

(4) PET-4: Al catalyst A PET sample was obtained according to the method shown below. That is,
To a heat medium circulation type (2 liter) stainless steel autoclave equipped with a stirrer, high-purity terephthalic acid and its 2-fold molar amount of ethylene glycol and triethylamine are added in an amount of 0.3 mol% with respect to the acid component. The esterification reaction was carried out for 120 minutes while distilling water out of the system at 245 ° C. under a pressure of 25 MPa to obtain an oligomer mixture. To this oligomer mixture, an aqueous solution of basic aluminum acetate (manufactured by Aldrich) and ethylene glycol are added as a polycondensation catalyst and cyclized. As a result, an ethylene glycol solution of 15 g / l basic aluminum acetate is added to the acid component in the polyester. 0.012 mol% as an aluminum atom and 0.02 mol% as Irganox 1425 were added to a 10 g / l ethylene glycol solution of Irganox 1425 (manufactured by Ciba Specialty Chemicals) as a phosphorus compound with respect to the acid component. Subsequently, it stirred at 245 degreeC for 10 minutes by the normal pressure in nitrogen atmosphere. Thereafter, while raising the temperature to 275 ° C. over 60 minutes, the pressure in the reaction system is gradually decreased to 13.3 Pa (0.1 Torr) until the desired IV is obtained at 275 ° C. and 13.3 Pa. A condensation reaction was carried out. When the predetermined stirring torque was reached, nitrogen was introduced into the autoclave to return to normal pressure, and the polycondensation reaction was stopped.

(5) PET-5: Ti catalyst According to the method shown below, a PET sample was obtained. In addition, in Table 1 below, those in which these are implemented are indicated as “Ti-2” in the “catalyst” column, and are shown separately from the Ti catalyst system PET (PET-1).

-Esterification reaction-
In the first esterification reactor, 4.7 tons of high-purity terephthalic acid and 1.8 tons of ethylene glycol are mixed for 90 minutes to form a slurry, and the first esterification reaction is continuously performed at a flow rate of 3800 kg / h. The tank was supplied. Furthermore, an ethylene glycol solution of a citrate chelate titanium complex (VERTEC AC-420, manufactured by Johnson Matthey) in which citric acid is coordinated to Ti metal was continuously supplied, and the average temperature was 250 ° C. with stirring in the reaction vessel. The reaction was carried out with a residence time of about 4.3 hours. At this time, the citric acid chelate titanium complex was continuously added so that the amount of Ti added was 9 ppm in terms of element. At this time, the acid value of the obtained oligomer was 600 eq / ton.

  This reaction product was transferred to a second esterification reaction vessel and reacted with stirring at a temperature in the reaction vessel of 250 ° C. and an average residence time of 1.2 hours to obtain an oligomer having an acid value of 200 eq / ton. The inside of the second esterification reaction tank is partitioned into three zones, and the ethylene glycol solution of magnesium acetate is continuously supplied from the second zone so that the amount of Mg added is 75 ppm in terms of element, From the three zones, an ethylene glycol solution of trimethyl phosphate was continuously supplied so that the amount of P added was 65 ppm in terms of element.

-Polycondensation reaction-
The esterification reaction product obtained above was continuously supplied to the first polycondensation reaction tank, with stirring, at a reaction temperature of 270 ° C. and a reaction tank internal pressure of 2.67 × 10 ⁻³ MPa (20 torr), Polycondensation was carried out with an average residence time of about 1.8 hours.

Furthermore, it was transferred to the second double condensation reaction tank, and the residence time was about 1.2 hours at a reaction tank temperature of 276 ° C. and a reaction tank pressure of 6.67 × 10 ⁻⁴ MPa (5 torr) with stirring in this reaction tank. The reaction (polycondensation) was carried out under the following conditions.

Subsequently, it was further transferred to the third triple condensation reaction tank. In this reaction tank, the reaction tank temperature was 278 ° C., the reaction tank pressure was 2.0 × 10 ⁻⁴ MPa (1.5 torr), and the residence time was 1.5 hours. Reaction (polycondensation) was carried out under conditions to obtain a reaction product (polyethylene terephthalate (PET)).

-2. Solid phase polymerization
The PET sample polymerized above was pelletized (diameter 3 mm, length 7 mm), and the obtained resin pellet was subjected to solid phase polymerization in a nitrogen atmosphere. At this time, the amount of terminal COOH and IV were adjusted as shown in Table 1 by appropriately changing the temperature and time during solid-phase polymerization. Further, the amount of fine powder contained in the pellet raw material was adjusted to the amount shown in Table 1 below by passing a cyclone after the solid phase polymerization and controlling the wind speed at that time.
In addition, TiO ₂ was added as a UV absorber after solid phase polymerization so as to have an amount shown in Table 1 below. Incidentally, the TiO ₂ is to create a master pellets in advance to a polyester resin by adding 20 mass% of TiO ₂ 2 screw extruder, this master pellet terms of TiO ₂ amount is an amount shown in Table 1 Was added as follows.

-3. Extrusion molding
Each PET sample that has been subjected to solid-state polymerization as described above is dried to a moisture content of 50 ppm or less, and then charged into a hopper of a single-screw kneading extruder having a diameter of 50 mm, and melted at 280 ° C. in a N ₂ stream. Extrusion was performed at 3 t / hr. After passing this melt (melt) through a gear pump and a filter (pore diameter 20 μm), it was extruded from a die having a width of 0.8 m under the following conditions, and the temperature was adjusted to 10 ° C. and having a diameter of 1.5 m. Cast on a cast roll (cooling roll).

<Condition>
[1] Shear rate at the time of melt extrusion from the die The melt extrusion rate and the width and height of the slit of the die are adjusted. Thereby, the shear rate described in Table 1 below was achieved. The shear rate (sec ⁻¹ ) is calculated by the following formula from the discharge amount Q (g / sec) of the extruder, the width W (cm) and the height H (cm) of the slit portion of the die.
Shear rate (sec ⁻¹ ) = {(Q / 1.1) / (W × H)} / H
[2] Cooling speed on cast roll The following methods (1) to (3) were selected and forcedly cooled until the melt on the cast roll cooled to 250 to 120 ° C. Specific methods are shown in Table 1 below.
(1) Cold air of 5 ° C. is applied onto the cast roll with an air knife at a wind speed of 20 m / s to forcibly cool the molten resin.
(2) Cool by touch roll. Specifically, the touch roll is cooled together with the cast roll, and the melt resin (melt) is sandwiched between the touch roll having a diameter of 50 cm adjusted to 5 ° C. and the cast roll and cooled from both sides of the melt.
(3) The melt on the cast roll is rapidly cooled by spraying cold water at 5 ° C.
[3] Vibration to Melt Vibration was applied as shown in Table 1 below by applying an eccentric rotating body to the bearing portion of the cast roll.
[4] Thickness of melt (unstretched film) extruded from die Adjust discharge amount of extruder and slit height of die. This adjusted to the melt thickness described in Table 1 below. The melt thickness was measured by photographing with a camera installed at the die exit.
[5] Abundance of unmelted material Unmelted material in an unstretched film after casting (before stretching) was measured. The measurement results are shown in Table 1 below.
In addition, the measurement sampled 10m < ² > which melted the melt rapidly on the cast roll, and counted the number of the foreign material on the light table visually. The number of foreign matters was divided by the mass (kg) of the sample to obtain the number of unmelted materials.

-4. Stretching and winding
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 2 below. The stretching was performed in the order of longitudinal stretching at 95 ° C. and transverse stretching at 140 ° C. in the order of longitudinal stretching and transverse stretching. Thereafter, the film was heat-fixed at 210 ° C. for 10 seconds and then relaxed by 3% in the lateral direction at 205 ° C. After stretching, both ends were trimmed by 10 cm, and after thicknessing was applied to both ends, 3000 m was wound around a resin core having a diameter of 30 cm. The width was 1.5 m and the winding length was 2000 m.
<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 3.5 times, and the stretching speed was 3000% / second.
(B) Transverse stretching The longitudinally stretched film was stretched laterally under the following conditions using a tenter.
<Condition>
-Preheating temperature: 110 ° C
-Stretching temperature: 120 ° C
-Stretch ratio: 3.9 times-Stretch speed: 70% / second

  The PET film for this invention and a comparison was produced as mentioned above. Next, the following evaluation was performed using the produced PET film.

-5. Evaluation of film
The physical properties (thickness, IV, amount of terminal COOH, water content, crystal orientation, birefringence, absorbance, elongation at break, withstand voltage, etc.) of the sample film produced as described above were measured. Each measurement result is shown in Table 2 below.
In addition, the measurement and evaluation of each physical property were performed by the following methods.

(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 amount of terminal carboxylic acid group (eq / t; = the amount of terminal COOH) was calculated from the appropriate amount.

(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.

(Moisture content)
The PET film was allowed to stand in an environment of 25 ° C. and 60% RH for 24 hours, and the moisture content of the PET film after being allowed to stand was measured using a Karl Fischer moisture meter (MKC-210 manufactured by Kyoto Electronics Co., Ltd.). . In addition, the PET film used for the measurement using the vaporizer (ADP-351 by Kyoto Electronics Co., Ltd.) and heating at 200 degreeC.

(Crystal orientation and its distribution)
The PET film was subjected to XD measurement, and the crystal orientation degree and crystal orientation degree distribution of the PET film were determined from the following formula.
Degree of crystal orientation = {peak intensity at 2θ = 23 ° ((110) plane)} / {peak intensity at 2θ = 25.8 ° ((100) plane)}
Crystal orientation degree distribution [%] = (Absolute value of difference between maximum value and minimum value of crystal orientation degree measured at points equally divided in width direction) / (Crystal orientation degree measured at each point equally divided in width direction 10) Average value) x 100

(Birefringence and its distribution)
The birefringence and birefringence distribution of the PET film were obtained from the following formula.
Birefringence = (nx + ny) / 2−nz
[Nx: refractive index in MD direction, ny: birefringence in TD direction, nz: birefringence in thickness direction]
Birefringence distribution [%] = (absolute value of difference between maximum and minimum values of birefringence measured at each point equally divided into 10 in the width direction) / (average of birefringence measured at each point equally divided into 10 in the width direction) Value) x 100

(Absorbance)
Absorbance at a wavelength of 380 nm was measured with a 300 μm thick PET film attached to the sample side of the spectrophotometer and the reference side as air.

(Breaking elongation retention time and its distribution)
Each PET 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 elongation at break of each thermo-treated sample was measured. Dividing by the breaking elongation before the thermo treatment, the breaking elongation retention at each thermo treatment time was determined from the following formula. Plotting the thermo-axis on the horizontal axis and the breaking elongation retention on the vertical axis, the results were tied to determine the heat treatment time [hr] at which the breaking elongation retention could be maintained at 10% or more.
Breaking elongation retention [%] = (breaking elongation after thermo treatment) / (breaking elongation before thermo treatment) × 100

(Withstand voltage characteristics)
About each PET film, the withstand voltage was calculated | required by measuring the voltage value which short-circuits according to JIST8010.

-6. Backsheet production
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>
-The above pigment dispersion: 71.4 parts-Polyacrylic resin aqueous dispersion: 17.1 parts (Binder: Jurimer ET410, manufactured by Nippon Pure Chemical Industries, Ltd., solid content: 30% by mass)
Polyoxyalkylene alkyl ether 2.7 parts (Naroacty CL95, manufactured by Sanyo Chemical Industries, solid content: 1% by mass)
Oxazoline compound (crosslinking agent) ... 1.8 parts (Epocross WS-700, manufactured by Nippon Shokubai Co., Ltd., solid content: 25% by mass)
・ Distilled water: 7.0 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 part (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 by mass (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.

-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.

-7. Fabrication 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. 1 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.

-8. Evaluation-
The following evaluation was performed about the back sheet produced as mentioned above and a solar cell module provided with the same. The evaluation results are shown in Table 2 below.

(Peeling)
After the solar cell module produced above is allowed to stand for 70 hours under an environmental condition of 120 ° C. and 100% RH, peeling between the backsheet and EVA (ethylene-vinyl acetate copolymer; sealant) occurs. The area of the area is measured. This measured value was calculated as a proportion of the total area of the solar cell module. The calculated value is shown as a percentage.

  As shown in Table 2, in the present invention, the occurrence of peeling was suppressed while achieving high withstand voltage characteristics, and a polyester film that could withstand long-term use was obtained. On the other hand, with the comparative polyester film, although a certain withstand voltage characteristic was obtained, it was impossible to fully prevent the occurrence of peeling.

  The PET film B-6 corresponds to Example 3 described in JP 2009-149065 A, whereas the PET film A-17 is melted corresponding to Example 3 of the publication. It is obtained by casting PET at an average cooling rate of 5 to 80 ° C./second at 250 to 120 ° C. In addition, the extending | stretching conditions in PET film A-17 and B-6 were implemented on the conditions as described in Example 1 of the said gazette.

  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

Claims (12)

  The heat treatment time (breaking elongation holding time) in which the thickness is 260 μm or more and 400 μm or less and the breaking elongation retention rate is maintained at 10% or more after heat treatment at 120 ° C. and 100% RH is 70 hours or more and 200 hours or less. Is a polyester film.   The polyester film according to claim 1, wherein the moisture content is 0.20% or more and 0.30% or less.   The polyester film according to claim 1 or 2, wherein the degree of crystal orientation is from 0.120 to 0.133, and the birefringence is from 0.1657 to 0.1690.   The polyester film according to any one of claims 1 to 3, wherein the crystal orientation degree distribution is 0.1% or more and 10% or less, and the birefringence distribution is 0.1% or more and 10% or less.   The amount of terminal carboxylic acid groups is 5 eq / t or more and 24 eq / t or less, The polyester film of any one of Claims 1-4.   The polyester film according to any one of claims 1 to 5, which has an intrinsic viscosity (IV) of 0.61 or more and 0.9 or less.   The polyester film according to any one of claims 1 to 6, which is obtained by using a titanium compound as a polymerization catalyst and contains 1 to 30 ppm of titanium atoms.   The polyester film according to any one of claims 1 to 7, wherein the absorbance at a wavelength of 380 nm is 0.001 or more and 0.1 or less. A resin containing polyester is melted, and the molten resin discharged in a strip shape having a thickness of 2600 μm or more and 6000 μm or less is subjected to an average cooling rate of 250 to 120 ° C. of the molten resin on a cooling roll of 5 to 80 ° C./second. Casting at a temperature of ℃ / second or less and applying vibration of 1 Hz to 100 Hz to the molten resin before casting until the temperature of the molten resin before casting reaches the glass transition temperature (Tg). A method for producing a polyester film by melt film formation.   The method for producing a polyester film according to claim 9, wherein the amount of unmelted material in the molten resin is 0.001 piece / kg or more and 0.1 piece / kg or less.   The solar cell backsheet provided with the polyester film of any one of Claims 1-8.   The solar cell module provided with the transparent board | substrate with which sunlight injects, a solar cell element, and the polyester film of any one of Claims 1-8.