WO2012102238A1

WO2012102238A1 - Polyester film, method for producing same, backsheet for solar cell, and solar cell power generation module

Info

Publication number: WO2012102238A1
Application number: PCT/JP2012/051350
Authority: WO
Inventors: 橋本　斉和; 山田　晃
Original assignee: 富士フイルム株式会社
Priority date: 2011-01-27
Filing date: 2012-01-23
Publication date: 2012-08-02
Also published as: JP5759908B2; JP2012166547A

Abstract

A method for producing a polyester film comprises: an extrusion step wherein polyester as a raw material is supplied to a venting type twin-screw extruder in which the inner diameter (D) of a cylinder is 140 mm to 300 mm inclusive, and under the conditions that an extrusion amount (Q) (kg/hr.) per unit time and a revolution number of screw (N) (rpm) satisfy the following formula (I), 0.01% to 5% of fluctuation is applied to the revolution number of screw (N) and a polyester sheet is melt-extruded; and a cooling/solidification step for cooling and solidifying the polyester sheet.

Description

POLYESTER FILM, ITS MANUFACTURING METHOD, SOLAR CELL BACK SHEET, AND SOLAR CELL POWER GENERATION MODULE

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

Polyester is used in various applications such as electrical insulation and optical applications. In recent years, solar cell applications such as solar cell backsheets have attracted attention as electrical insulation applications.
By the way, polyester usually has many carboxyl groups and hydroxyl groups on its surface, and tends to be hydrolyzed in an environment where moisture exists, and tends to deteriorate over time. The environment in which solar cell modules are generally used is an environment that is constantly exposed to wind and rain, such as outdoors, and is an environment that is prone to hydrolysis. one of.

The polyester film is produced by stretching an extruded polyester sheet. In general, the polyester sheet is formed by extruding a polyester molten sheet onto a casting drum surface and cooling and solidifying. However, a vent type twin-screw extruder may be used as an extruder (molding machine) (for example, JP-A-10-95042). The vent type twin screw extruder is an extruder having a vent hole for degassing by depressurizing action. When the raw material polyester is put into the extruder, air and volatile components taken together are introduced from the vent hole. Can be removed.

However, in Japanese Patent Application Laid-Open No. 10-95042, since the exhaust is evacuated through the vent hole, the melted polyester (also referred to as “melt”) in the extruder tends to stay in the extruder, and the polyester Foreign matter due to thermal deterioration was easily generated in the polyester. If the foreign matter remains in the polyester when the polyester is stretched after the polyester is extruded from the extruder, stretching unevenness is likely to occur.

The present invention aims to provide a polyester film in which stretching unevenness is suppressed, a method for producing the same, and a solar cell backsheet in which weather resistance unevenness is suppressed, and to achieve the object.

Specific means for achieving the above object are as follows.
<1> The raw material polyester is supplied to a vent type twin screw extruder having a cylinder inner diameter D of 140 mm or more and 300 mm or less, the cylinder inner diameter D, the extrusion amount Q (kg / hr.) Per unit time, and the screw rotation speed. Extrusion step of melt-extruding a polyester sheet by giving a fluctuation of 0.01% to 5% to the screw rotation speed N under the condition that N (rpm) satisfies the following formula (I); It is the manufacturing method of the polyester film including the cooling solidification process which cools and solidifies a polyester sheet.

<2> In the waveform representing the screw rotational speed N with respect to time, the half-value width of the peak representing the rotational speed that is ± 0.1% to ± 3% of the average value of the screw rotational speed N is the screw rotational speed. It is a manufacturing method of the polyester film as described in said <1> which is 1/100 or more and 1/4 or less of the reciprocal number of the average value of N.

<3> The polyester film according to <1> or <2>, wherein the raw material polyester includes 0.01% by mass to 5% by mass of polyester powder with respect to the total mass of the polyester pellets and the polyester pellets. It is a manufacturing method.

<4> The extrusion process is the method for producing a polyester film according to any one of <1> to <3>, wherein the polyester sheet further gives a thickness variation of 1% to 30% to the melt-extruded polyester sheet. .

<5> In addition, a melt-extruded polyester sheet is conveyed, and includes a stretching step in which a polyester film is obtained by longitudinal stretching and lateral stretching,
In the longitudinal stretching, when the stretching of the polyester sheet is started, the transport speed of the polyester sheet is set to 30 m / min to 100 m / min, and the transport speed is varied by 0.01% to 1%. The method for producing a polyester film as described in any one of <1> to <4>.

<6> In the waveform representing the transport speed with respect to time, the half width of the peak representing the transport speed that is ± 0.1% to ± 1% of the average value of the transport speed is the reciprocal of the average value of the transport speed. It is a manufacturing method of the polyester film as described in <5> which is 1/100 or more and 1/4 or less.

<7> The longitudinal stretching is performed by giving a temperature distribution of 0.1 ° C. to 30 ° C. in the thickness direction of the polyester sheet to the polyester sheet when stretching of the polyester sheet is started. <6> A method for producing a polyester film according to <6>.

<8> The lateral stretching is performed by grasping an end portion of the polyester sheet, widening the polyester sheet in a direction orthogonal to the conveying method, and 0.1% to 5% in the conveying speed of the polyester sheet. %. The method for producing a polyester film according to any one of <5> to <7>, wherein the production is performed with a variation of%.

<9> In the waveform representing the conveyance speed with respect to time, the half width of the peak representing the conveyance speed that is ± 0.1% to ± 5% of the average value of the conveyance speed is the reciprocal of the average value of the conveyance speed. It is a manufacturing method of the polyester film as described in said <8> which is 1/100 or more and 1/4 or less.

<10> The polyester film according to any one of <5> to <9>, wherein the thickness of the biaxially stretched polyester film subjected to the longitudinal stretching and the lateral stretching is 30 μm to 400 μm. It is a manufacturing method.

<11> The method for producing a polyester film according to any one of <1> to <10>, wherein the raw material polyester contains 1 ppm to 50 ppm of titanium element.

<12> In the extrusion step, the temperature of the raw material polyester in the vented twin-screw extruder is set to 300 ° C. to 350 ° C. for 1 second to 10 minutes, and then cooled to 290 ° C. or lower. The method for producing a polyester film according to any one of <1> to <11>, wherein the polyester sheet is melt-extruded.

<13>
The method for producing a polyester film according to any one of <1> to <12>, wherein the occurrence frequency of fluctuation in the screw rotation speed N is 0.01 times / second to 50 times / second.
<14>
The method for producing a polyester film according to <8>, wherein the occurrence frequency of fluctuation in the polyester sheet conveying speed is 0.01 times / second to 50 times / second.
<15>
A polyester film produced by the method for producing a polyester film according to any one of <1> to <14>.

<16>
It is a solar cell backsheet using the polyester film as described in said <15>.
<17>
A solar cell power generation module including a laminate in which a transparent substrate and the solar cell backsheet described in <16> are bonded to each other with a solar cell element interposed therebetween.

According to the present invention, it is possible to provide a polyester film in which stretch unevenness is suppressed, a method for producing the same, and a solar cell backsheet in which weather resistance unevenness is suppressed.

It is a side view of a vent type twin screw extruder. It is a top view of a biaxial stretching machine. It is a top view of the biaxial stretching machine which connected the vent type biaxial extruder, the longitudinal stretching apparatus, and the transverse stretching apparatus in series. It is a side view of the biaxial stretching machine which connected the bent type biaxial extruder, the longitudinal stretching apparatus, and the horizontal stretching apparatus in series. It is an example of the waveform showing the screw speed N with respect to the time of this invention. It is another example of the waveform showing the screw speed N with respect to the time of this invention.

<Production method of polyester film>
The production method of the polyester film of the present invention is such that the raw material polyester is supplied to a vent type twin-screw extruder having a cylinder inner diameter D of 140 mm or more and 300 mm or less, and the cylinder inner diameter D and the extrusion amount Q (kg / hr per unit time). .) And the screw rotation speed N (rpm) satisfy the following formula (I) to give a fluctuation of 0.01% to 5% to the screw rotation speed N to melt the polyester sheet The composition includes an extruding step of extruding and a cooling and solidifying step of cooling and solidifying the polyester sheet.

In the present invention, when the raw material polyester is supplied under the condition satisfying the above formula (1) using a vent type twin screw extruder having a cylinder inner diameter D of 140 mm or more and 300 mm or less, the screw rotation speed N is 0.01% to By giving a 5% variation and melt-extruding the polyester sheet, it is possible to produce a polyester film while suppressing the remaining foreign matter in the polyester.
Although it is not certain why the production of the polyester film of the present invention has the above configuration, the generation of foreign matters in the polyester film is not clear, but it is presumed to be due to the following reason. The vent type twin-screw extruder may be simply referred to as “extruder”.

As described above, the vent type twin-screw extruder is provided with a vent hole 10 for deaeration by depressurization in a cylinder having a screw, and the inside of the cylinder and the outside of the cylinder are connected via the vent hole. Communicates. The vent hole is also referred to as “vent port” [JIS B8650: 2006, a) Extruder, see number 115].

The raw material polyester put into the extruder is heated and melted by being kneaded by the screw 6 and gradually becomes a melt. When the melt is pushed to the vicinity of the vent hole and the pressure is reduced from the vent hole, the melt is sucked to the vent hole, so that the melt flow is poor in the vicinity of the vent hole, and the melt tends to stay. For this reason, the melt sticks in the vicinity of the vent and is heated as it is, so that thermal decomposition easily occurs. It is considered that the thermal decomposition component adhering to the vicinity of the vent is peeled off by the melt that is sequentially washed away and is taken into the melt as “foreign matter”.
When such a foreign material was taken into the melt and extruded from an extruder to become a polyester sheet, uneven stretching occurred due to the foreign material when the polyester sheet containing the foreign material was stretched. More specifically, stretching unevenness caused by foreign matter is more easily stretched in a portion of the polyester sheet where no foreign matter is present, and the portion where the foreign matter is present and the vicinity thereof are less likely to be stretched. A phenomenon in which a film becomes a polyester film having a different thickness depending on the location.

This stretching unevenness can be measured from the non-uniformity of the size of the mesh after the polyester sheet is stretched and the polyester sheet is stretched.
In addition, the foreign material which causes the stretching unevenness is not only a thermal decomposition component of the polyester generated in the above-described extruder, but also a polyester crystal (spherulite). The method for suppressing the spherulite will be described later.

On the other hand, in the present invention, in melt kneading with a screw, a fluctuation of 0.01% to 5% is imparted to the screw rotation speed (N). That is, the extrusion is not continued while keeping the screw speed constant, but the screw speed is increased or decreased within a range of 0.01% to 5%. It is considered that the vibration is given to the melt because the flow of the melt in the cylinder is accelerated or suppressed by changing the screw rotation speed. And it is thought that the foreign material in a melt and the foreign material adhering to vent-hole vicinity are grind | pulverized by this vibration.
Therefore, according to the method for producing a polyester film of the present invention, foreign matter hardly remains in the melt-extruded polyester, and when the melt-extruded polyester (sheet) is stretched, uneven stretching due to the foreign matter is suppressed. It is thought that it can be done.

In the present invention, the polyester to be fed into the extruder is “raw polyester”, the polyester after being extruded from the extruder, and the polyester to be stretched is “polyester sheet”. This polyester is called “polyester film”. Therefore, even if the polyester has been subjected to longitudinal stretching and lateral stretching, the polyester to be further stretched is referred to as a polyester sheet in the present specification.
Hereafter, the detail of the manufacturing method of the polyester film of this invention is divided and demonstrated to each item of an extrusion process, a vent type biaxial extruder, raw material polyester, and an extending process.

[Extrusion process]
In the extrusion process, the raw material polyester is supplied to a vent type twin screw extruder having a cylinder inner diameter D of 140 mm or more and 300 mm or less, the cylinder inner diameter D, the extrusion amount Q (kg / hr.) Per unit time, and screw rotation. The number N (rpm) is a step of melt-extruding the polyester sheet by imparting a variation of 0.01% to 5% to the screw rotational speed N under the condition satisfying the following formula (I).

As described above, in the extrusion step, the raw material polyester is melt-kneaded using an extruder that operates a screw under specific conditions.
The extrusion process may further include a cooling process for cooling the temperature of the polyester in the extruder.

(Bent type twin screw extruder)
The vent type twin-screw extruder according to the present invention includes at least a cylinder having an inner diameter D of 140 mm or more and 300 mm or less and two screws. Further, the cylinder inner diameter D, the extrusion amount Q (kg / hr.) Per unit time, and the screw rotation speed N (rpm) operate under the conditions satisfying the above formula (I), and further the screw rotation speed. N is given a variation of 0.01% to 5%.
FIG. 1 shows an example (side view) of a vent type twin screw extruder.
As shown in FIG. 1, the vent type twin screw extruder 100 (extruder 100) has at least a hopper 2, a cylinder 4, a screw 6, a reverse screw screw 8, a vent hole 10, and an extrusion port 12. The screw 6 is rotated by the driving device M.

The hopper 2 is an inlet for raw material polyester, and the raw material polyester charged into the extruder 100 from the hopper 2 is transferred toward the extrusion port 12 while being kneaded by the cylinder 4.
The raw material polyester is heated by a temperature control device (not shown) of the extruder 100 and is sheared by the screw 6 and the reverse screw screw 8, so that the cylinder 4 and the screw 6 among the supplied raw material polyesters. It gradually plasticizes from the part in contact with etc. and melts into a melt (molten resin). The vent hole 10 is connected to a decompression device (decompression pump or the like) (not shown), and the air taken into the extruder 100 when the raw material polyester is charged, the moisture generated during the melt kneading of the raw material polyester, etc. Removed from 10.
Eventually, the melt is extruded out of the extruder 100 from the extrusion port 12, and is formed into a sheet shape by a casting drum or the like (not shown), and is cooled and solidified.
Hereinafter, description will be made with the number omitted.

The cylinder is also referred to as a barrel (see JIS B8650: 2006, a) Extruder, No. 110), and may be provided with a temperature control device for heating or cooling the raw material polyester flowing in the cylinder.
In the present invention, the inner diameter (diameter) D of the cylinder is 140 mm or more. When the inner diameter D of the cylinder is smaller than 140 mm, the surface area of the melt in the extruder 100 increases. That is, since the amount of the raw material polyester that comes into contact with the screw or the cylinder increases and it becomes easy to receive shearing heat generation, foreign matters are easily generated due to thermal decomposition.
The inner diameter D of the cylinder is preferably 150 mm to 300 mm, more preferably 160 mm to 260 mm. If the inner diameter D of the cylinder exceeds 300 mm, the resin tends to stay in the gap between the screw and the barrel, which increases with the screw diameter, and easily becomes a foreign matter.

In FIG. 1, the vent hole is located on the downstream side (extrusion port side) from the position where the reverse screw is provided, and only one is provided in the extruder, but is located on the more upstream side. In addition to the vent hole shown in FIG. 1, one or more vent holes may be provided between the vent hole and the extrusion port.
In the present invention, the vent hole is preferably installed at a position 1/3 of the total length L of the cylinder as measured from the inlet side 14 of the cylinder. The total length L of the cylinder refers to the length inside the cylinder, and refers to the distance between the end portion (entrance side 14) where the raw material polyester enters and the end portion on the extrusion port 12 side.

The extruder includes two screws (two axes), and the screws may rotate in the same direction or in different directions. Further, a meshing type in which two screws are close to each other and the teeth of the screw mesh with each other may be used, or a non-meshing type in which the teeth are not meshed with each other may be used.
The screw may be composed of only a forward screw for transferring the raw material polyester to the extrusion port, or as shown in FIG. May be.

The screw transfers the raw polyester according to the rotational speed N (rpm), and the extrusion amount Q (kg / hr.) Per unit time of the polyester sheet melt-extruded from the extruder changes. Here, in the present invention, the inner diameter D of the cylinder, the screw rotation speed N, and the extrusion amount Q per unit time of the melt satisfy the following formula (I).

Here, Q / N is the extrusion amount (discharge amount) per one screw rotation, and it is preferable to increase this value in proportion to the 2.8th power of the inner diameter D of the cylinder. That is, it is preferable to increase the Q / N within a range that is proportional to the 2.8th power of the inner diameter D of the cylinder, because shear heat generation can be suppressed.
The volume in which the polyester (melt) in the extruder is conveyed as the cylinder inner diameter D increases is proportional to the cube of D. Since it was found empirically, the amount of Q / N is specified in a range proportional to D to the 2.8th power. The coefficient of “D ^2.8 ” shown in the formula (I) is a boundary value obtained from experiments and the occurrence of foreign matter.

By satisfying the formula (I), it is possible to increase the deaeration efficiency while suppressing excessive heat generation due to the shearing action of the screw, and to prevent a decrease in intrinsic viscosity (IV) of the polyester.
When Q / N exceeds “15.8 × 10 ⁻⁶ × D ^2.8 ”, the rotation speed is low and the shear is low, and the melt in the cylinder tends to stay near the vent hole and melts, that is, melts. Since thermal decomposition of polyester occurs, foreign matter increases. On the other hand, when the Q / N is less than “5.2 × 10 ⁻⁶ × D ^2.8 ”, the high rotational speed and the high shear are generated, the melt is subjected to shearing heat generation, and is easily thermally decomposed to increase foreign matters.
Q / N preferably satisfies the following formula (II), and more preferably satisfies the following formula (III).

Further, in the present invention, the screw is driven within the range satisfying the above formula (I), and a fluctuation of 0.01% to 5% is given to the screw rotation speed N.
By giving fluctuation to the screw rotation speed N, it is possible to vibrate the melt adhering to the vent hole and to suppress the stagnation of the melt. As a result, since the thermal decomposition of the melt can be suppressed, the generation of foreign matters can be suppressed. Even when foreign matter is taken into the melt, the foreign matter in the melt is vibrated by changing the screw rotational speed N, so that the foreign matter can be crushed.
Therefore, even when the melt is extruded from the extruder and the polyester molded into a sheet is stretched, stretching unevenness due to foreign matters can be suppressed.

In the present invention, “adding a fluctuation of 0.01% to 5% to the screw rotation speed N” specifically means that the screw rotation speed is set to 0.01 than the screw rotation speed satisfying the formula (I). % To 5% higher (accelerating the melt transfer speed) and the screw speed to 0.01% to 5% smaller than the screw speed satisfying the formula (I) ( Reducing the melt transfer speed). In the present invention, from the viewpoint of the crushing force of foreign matter, the screw rotation speed is set to 0.01% to 5% higher than the screw rotation speed satisfying the formula (I) (the melt transfer speed is accelerated). It is more preferable.

The fluctuation of the screw speed N can be achieved by giving a fluctuation to the current value of the screw driving device. The fluctuation is the difference between the maximum speed and the minimum speed during one minute divided by the average value and expressed as a percentage, and the fluctuation occurrence frequency [times / second] may be in the range of 0.01-50. Preferably, 0.1 to 10 is more preferable.
In addition, it is preferable to add the fluctuation | variation of the screw speed N to a spike shape, and to give discontinuously.
The fluctuation of the screw rotation speed N is preferably 0.1% to 3%, and more preferably 0.3% to 1%.

The fluctuation of the screw rotation speed N indicates that the half width of the peak representing the screw rotation speed that is ± 0.1% or more of the average value of the screw rotation speed N in the waveform representing the screw rotation speed N with respect to time is the screw rotation speed N. It is preferable to give so that it may become 1/4 or less of the reciprocal number of the average value.
Here, in the “waveform representing the screw rotation speed with respect to time”, the “peak” means a maximum waveform or a minimum waveform having a rotation speed that is ± 0.1% or more of the average value (Nave) of the screw rotation speed N. Point to.
Therefore, “the peak representing the screw rotation number that is ± 0.1% or more of the average value of the screw rotation number N” specifically means “+ 0.1% or more of the average value of the screw rotation number N”. It represents at least one of a peak representing the screw rotation speed (maximum peak) and a “peak representing the screw rotation speed that is −0.1% or more of the average value of the screw rotation speed N (minimum peak)”.
Further, the average value of the screw rotation speed N refers to “an average value of the screw rotation speed N in an arbitrary 10 minutes”.

In other words, the reciprocal of the screw rotation speed N [rpm] means the time [minute] required for one screw rotation. Accordingly, when the half-width of the peak is Δt and the time [minute] required for one rotation of the screw is t, “less than 1/4 of the reciprocal of the average value of the screw rotation speed N” is Δt ≦ t × 1/4. That is, it can be approximated as Δt / t ≦ 1/4.

The timing which gives a fluctuation | variation to screw rotation speed is demonstrated using FIG.
FIG. 4 shows an example of a waveform in which the vertical axis represents the screw rotation speed and the horizontal axis represents time. The shape of the waveform shows a locus (plot group) when the screw rotation speed is plotted against time, in other words, the fluctuation of the screw rotation speed. If the trajectory when the screw rotation speed is plotted against time is a straight line parallel to the time axis (horizontal axis), it means that the screw rotation speed is constant and does not vary. On the other hand, when the locus of the plot goes up and down in a wave shape, it means that the screw rotation speed fluctuates. Furthermore, for example, when the screw rotation speed suddenly increases and decreases rapidly like a pulse wave represented as a maximal waveform, the screw rotation speed must be rapidly increased and returned to its original value rapidly. means.

Here, the waveform shown in FIG. 4 is a waveform that rises and falls in the vicinity of the average value (Nave) of the screw rotation speed, and the screw rotation speed increases abruptly, and abruptly reaches the maximum value (Nmax) as a boundary. A reduced protuberance maximum waveform is shown. Such a waveform is also referred to as “spike”. FIG. 4 shows a maximum peak in which the maximum rotation speed is + 0.1% or more than the average value of the screw rotation speed. In the present invention, it is lower than the average rotation speed of the screw. A peak (minimum peak) protruding 0.1% or more on the side (minus side) is also included in the “peak”.

The minimum peak will be described with reference to FIG.
FIG. 5 shows an example of a waveform in which the vertical axis represents the screw speed and the horizontal axis represents time, as in FIG. Two types of waveforms are shown. One (left side) shows a minimum peak P1, and the other (right side) shows a waveform in which a minimum peak P2 and a maximum peak P3 are continuous.
The minimum peak is a waveform protruding 0.1% or more below (minus side) the average value (Nave) of the number of screw rotations as indicated by P1 on the left side of FIG. It is shown as a projection-like minimal waveform that rapidly decreases with the minimum value (Nmin) as the rotational speed decreases rapidly.
When the half-value width of the minimum peak P1 shown in FIG.
The waveforms on the right side of FIG. 5 (P2 and P3) will be described later.

The maximum value (Nmax) of the maximum peak is preferably + 0.1% to + 0.3% of the average value (Nave) of the screw rotation speed, and the minimum value (Nmin) of the minimum peak is the average value of the screw rotation speed. The value (Nave) is preferably -0.1% to -0.3%.

Immediately after giving the fluctuation on the acceleration side that becomes the maximum waveform, the fluctuation of the screw rotation speed gives the fluctuation on the deceleration side that becomes the minimum waveform, or on the contrary, immediately after giving the fluctuation on the deceleration side that becomes the minimum waveform, You may give the acceleration side fluctuation | variation used as a maximum waveform. In this case, when the half-value width of the maximum waveform is Δt1 and the half-value width of the minimum waveform is Δt2, (Δt1 + Δt2) may be equal to or less than ¼ of the reciprocal of the average value of the screw rotation speed.
Thus, in the case of giving a variation in which the maximal waveform or the minimal waveform is made continuous, the sum (ΣΔt) of each half-value width Δt of the continuous maximal waveform or the minimal waveform is ¼ or less of the reciprocal of the average value of the screw rotation speed. It only has to be.

The change in the screw rotation speed waveform in the case where the acceleration-side variation having the maximum waveform is applied immediately after the deceleration-side variation having the minimum waveform will be described with reference to FIG.
On the right side of FIG. 5, an example of a waveform in which a minimum peak P2 that is a minimum waveform and a maximum peak P3 that is a maximum waveform are adjacent to each other is shown. As described above, when the acceleration-side variation having the maximum waveform is applied immediately after the deceleration-side variation having the minimum waveform is applied, the minimum peak P2 and the maximum peak P3 appear continuously.
When the fluctuation represented by the waveform shown on the right side of FIG. 5 is given to the screw rotation speed, it is the sum of Δt2 that is the half-value width of the minimum peak P2 and Δt3 that is the half-value width of the maximum peak P3 (Δt2 + Δt3). May be ¼ or less of the reciprocal of the average value of the screw rotation speed.

In order to rapidly increase or decrease the screw rotation speed N, it is preferable that the half-value width Δt of the peak of the waveform representing the screw rotation speed N with respect to time be ¼ or less of the inverse of the average value of the screw rotation speed N. The half width Δt of the peak is more preferably 1/10 or less of the inverse of the average value of the screw rotation speed N.
As shown in the spike-like waveform shown in FIG. 4 or FIG. 5, it is preferable that vibration can be applied to the melt more efficiently by intermittently applying vibration to the screw rotation speed N.

Next, the temperature conditions of the raw material polyester in the extrusion process and other preferred embodiments will be described.

(Temperature conditions)
The melting temperature of the raw material polyester may be a temperature equal to or higher than the melting point (Tm) of the raw material polyester, for example, Tm + 10 ° C. or higher. To make the polyester sheet produced through the extrusion process thick (for example, 3 mm or higher) The extrusion process is preferably performed under the following temperature conditions.
That is, the extrusion step is preferably performed under a temperature condition in which the temperature of the raw material polyester in the vent type twin screw extruder is set to 300 ° C. to 350 ° C. for 1 second to 10 minutes and then lowered to 290 ° C. or less. .
The heating time is more preferably 2 seconds or more and 5 minutes or less, and further preferably 3 seconds or more and 3 minutes or less.

The melt melt-extruded from the extruder onto a cooling member such as a cast drum is cooled, solidified, and formed into a sheet, but with a thick polyester sheet, the cast thickness is thick and cooling is delayed due to large heat storage. . As a result, crystals (spherulites) in the polyester sheet grow and contribute to stretching unevenness when the polyester sheet is stretched.
In order to suppress stretching unevenness due to the presence of grown spherulites, it is effective to expose the raw material polyester to 300 ° C. or higher as described above. As a result, the spherulites present in the raw material polyester can be completely melted at the molecular level, or the crystals can be made smaller. Therefore, even if the polyester sheet extruded on the cast drum is thick, it is difficult to generate stretching unevenness in the stretching process.
Usually, melting of polyethylene terephthalate (PET) crystals occurs at 250 ° C. to 260 ° C., but it has been found in the present invention that at least 300 ° C. is required to completely melt the crystals to the molecular level.
Such raw material polyester crystals are usually produced during the drying step of drying the raw material polyester before the raw material polyester is put into the hopper. However, even if the raw material polyester is not dried, the crystals are formed in the polyester. May be generated. The raw material polyester charged into the extruder through the hopper is heated in the extruder and passes through the crystallization temperature while the temperature of the raw material polyester is rising. Spherulites) may form.

When the polyester containing spherulites formed as described above is heated at 300 ° C. to 350 ° C. for 1 second to 10 minutes, the crystals melt or the crystals can be reduced. During cooling, it is possible to suppress the growth of spherulites due to the remaining structure of spherulites. If the heating time of the raw material polyester is less than the above time, melting will be insufficient, and spherulites will easily grow due to the residual structure of the spherulites in the polyester. Both are easy to cause unevenness in stretching.

The raw material polyester heated at the above heating time (1 second to 10 minutes) and at the above heating temperature (300 ° C. to 350 ° C.) can then be cooled under a temperature decreasing condition of 290 ° C. or less, more preferably 280 ° C. or less. preferable. Thereby, generation | occurrence | production of the foreign material by thermal decomposition of a melt can be suppressed. Specifically, the temperature of the raw material polyester may be controlled by, for example, installing a heater or a refrigerant pipe covering a part or all of the outside of the cylinder in the cylinder of the extruder.

Also, from the viewpoint of suppressing thermal decomposition (polyester hydrolysis) in the extruder, it is preferable to perform melt extrusion of the raw material polyester by replacing the inside of the extruder with nitrogen.

The melted raw material polyester (melt) is extruded from an extrusion die through a gear pump, a filter or the like. The extrusion die is also simply referred to as “die” (see JIS B 8650: 2006, a) extrusion molding machine, number 134).
At this time, the melt may be extruded as a single layer or may be extruded as a multilayer.

The melt (polyester) extruded from the die is formed into a sheet having a thickness of 3 mm to 5 mm, preferably 3.2 mm to 4.7 mm, more preferably 3.4 mm to 4.6 mm. By setting the thickness of the polyester sheet to 5 mm or less, it is possible to avoid a cooling delay due to heat storage of the melt and to suppress the formation of spherulites due to the cooling delay. Moreover, by setting the thickness of the melt to be extruded to 3 mm or more, OH groups and COOH groups in the polyester are diffused into the polyester during the period from extrusion to cooling, and OH groups and COOH cause hydrolysis. Suppresses exposure of the group to the polyester surface. Further, when the polyester sheet is stretched to obtain a polyester film, a biaxially stretched polyester film having a thickness of 100 μm or more can be obtained even if the stretching ratio is increased. Moreover, when the thickness of the polyester sheet is 3 mm or more, it is easy to express electrical insulation, and it is suitable for solar cell backsheet applications.

(Thickness variation)
In the extrusion step, it is further preferable to give a thickness variation of 1% to 30% to the melt-extruded polyester sheet.
By giving a thickness variation (thickness unevenness) of 1% to 30% to the polyester sheet melt-extruded from the extruder by the above-described method, the stretching stress fluctuates and increases when the polyester sheet is stretched. Decrease. When the stretching stress increases, stress concentration occurs around the foreign material (residues of pyrolysis components generated in the extruder or grown spherulites), and the vicinity of the foreign material is also stretched to reduce stretching unevenness.

Such thickness variation may be in the conveyance direction (MD) of the polyester sheet or in any direction of the direction (TD) orthogonal to the conveyance direction.
The thickness variation can be imparted by varying the number of rotations of the screw of the extruder or by vibrating the extrusion die. For example, thickness fluctuation can be given to MD direction of a polyester sheet by giving fluctuation to the number of rotations of the screw of an extruder. On the other hand, the thickness variation in the TD direction of the polyester sheet can be imparted by vibrating the extrusion die after the melt is extruded from the extruder.
The variation amount of the thickness (cast thickness) of the polyester sheet is more preferably 2% to 25%, and further preferably 3% to 20%.

[Cooling and solidification process]
The cooling and solidifying step is a step of cooling and solidifying the polyester sheet melt-extruded by the extrusion step.
The means for cooling the melt extruded from the extrusion die is not particularly limited, and it is sufficient to apply cold air to the melt, bring it into contact with a cast drum (cooled cast drum), or spray water. Only one cooling means may be performed, or two or more cooling means may be combined.
Among the above, the cooling means is preferably at least one of cooling by cold air and cooling using a cast drum from the viewpoint of preventing oligomer adhesion to the sheet surface during continuous operation. Furthermore, it is particularly preferable that the melt extruded from the extruder is cooled with cold air, and the melt is brought into contact with the cast drum and cooled.

Moreover, the polyester cooled using the cast drum etc. is peeled off from cooling members, such as a cast drum, using peeling members, such as a peeling roll.
Next, the detail of raw material polyester is demonstrated.

(Raw material polyester)
The raw material polyester is not particularly limited as long as it is a raw material for the polyester sheet and the polyester film and contains polyester, and may contain a slurry of inorganic particles or organic particles in addition to the polyester. The raw material polyester may contain a titanium element derived from the catalyst.
First, the raw material polyester will be described from the viewpoint of the form when it is put into an extruder, and then will be described from the viewpoint of components such as polyester and additives.

The form of the raw material polyester to be fed into the extruder is preferably a pellet from the viewpoint of ease of plasticization and melting.
Moreover, 2 or more types of polyester which has a different bulk density can also be used for polyester contained in raw material polyester. Specifically, recycled polyester can be used for a part of the polyester.
By the way, the so-called fluff obtained by pulverizing the end of the film into small pieces among the recycled polyester has a bulk density in the range of 0.01 to 0.60, and has a problem that it stays in the supply port without being well bitten by the screw. . In addition, in the case of a material having a low bulk density as described above, the pressure fluctuation at the tip of the extruder becomes large because the transportation efficiency with the pellet differs in the screw transportation section, and as a result, the fluctuation in the amount of extrusion also increases. Therefore, it is difficult to use a fluff having a low bulk density as described above on a chip production line dedicated to the fluff.

However, according to the present invention, at least one polyester has a bulk density of 0.01 to 0.60, and two or more polyesters having different bulk densities can be melt-extruded without any problem. it can. That is, according to the present invention, the pressure fluctuation at the tip of the extruder is ± 5 kg / cm ² or less, and the surface area of the melt at the vent hole is increased, so that the deaeration efficiency is improved, especially the intrinsic viscosity of the polyester. The retention rate is improved, and the decrease in intrinsic viscosity after melt extrusion can be suppressed to 10% or less.

The conditions shown in the above-described formula (I) are particularly effective when the intrinsic viscosity of the polyester having the smallest bulk density is smaller than the intrinsic viscosity of other polyesters. The bulk density at that time is preferably 0.6 or less. When the bulk density is larger than 0.6, the effect of improving the retention rate of intrinsic viscosity becomes poor. On the contrary, when the bulk density is less than 0.01, the volume of the polyester increases, so that it is difficult to ensure a sufficient amount of raw material supply, and problems such as raw material blockage occur in the supply pipe. It becomes easy. The blending amount of the polyester having a bulk density of 0.01 to 0.60 is usually 60% or less, preferably 55% or less, more preferably 50% or less based on the total polyester.

The bulk density of the polyester can be measured by a method in accordance with JIS K7365: 1999 “Plastics—Determination of apparent density of material that can be poured from specified funnel”.

In general, only the pellets are charged into the extruder. In the present invention, in order to suppress the generation of foreign matters in the extruder, it is preferable to mix the polyester powder together with the pellets in the raw material polyester. When such a powder is added, the torque of the screw fluctuates when the screw bites into the raw material polyester. As a result, the polyester in contact with the screw vibrates and suppresses the stagnation of the melt in the vicinity of the vent hole. Such a polyester powder can be obtained by crushing raw material polyester pellets to be used and then sieving them, and it is preferable to use a 30-300 mesh one.
The polyester powder used together with the pellets is preferably 0.01% by mass to 5% by mass, more preferably 0.03% by mass to 3% by mass with respect to the total mass of the raw material polyester pellets. More preferably, it is 0.05 mass% to 1 mass%.

As described above, recycled polyester obtained by regenerating used polyester may be used as the raw material polyester. The pelletized polyester may be a regenerated polyester, or the polyester on the powder may be a regenerated polyester. The amount of recycled polyester used is preferably 5% by mass to 50% by mass, more preferably 10% by mass to 45% by mass, and more preferably 20% by mass to 40% by mass with respect to the total mass of the raw material polyester. It is more preferable.
Next, raw material polyester is demonstrated from a viewpoint of a component.

The kind of polyester contained in the raw material polyester is not particularly limited.
It may be synthesized using a dicarboxylic acid component and a diol component, or a commercially available polyester may be used.

When the polyester is synthesized, for example, it can be obtained by subjecting (A) a dicarboxylic acid component and (B) a diol component to an esterification reaction and / or a transesterification reaction by a known method.
(A) Examples of the dicarboxylic acid component include malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecanedioic acid, dimer acid, eicosandioic acid, pimelic acid, azelaic acid, methylmalonic acid Aliphatic dicarboxylic acids such as ethylmalonic acid, adamantane dicarboxylic acid, norbornene dicarboxylic acid, isosorbide, cyclohexanedicarboxylic acid, decalin dicarboxylic acid, and the like, terephthalic acid, isophthalic acid, phthalic acid, 1,4- Naphthalene dicarboxylic acid, 1,5-naphthalene dicarboxylic acid, 2,6-naphthalene dicarboxylic acid, 1,8-naphthalene dicarboxylic acid, 4,4′-diphenyl dicarboxylic acid, 4,4′-diphenyl ether dicarboxylic acid, 5-sodium sulfo Isophthalic acid, phenyl ether Boy carboxylic acid, anthracene dicarboxylic acid, phenanthrene carboxylic, 9,9'-bis (4-carboxyphenyl) a dicarboxylic acid or its ester derivatives such as aromatic dicarboxylic acids such as fluorene acid.

(B) Examples of the diol component include fats such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-butanediol, and 1,3-butanediol. Diols, cycloaliphatic dimethanol, spiroglycol, isosorbide and other alicyclic diols, bisphenol A, 1,3-benzenedimethanol, 1,4-benzenedimethanol, 9,9'-bis (4-hydroxyphenyl) ) Diol compounds such as aromatic diols such as fluorene.

(A) As a dicarboxylic acid component, the case where at least 1 sort of aromatic dicarboxylic acid is used is preferable. 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.
Moreover, it is preferable that at least one aliphatic diol is used as the (B) 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.

A conventionally known reaction catalyst can be used for the esterification reaction and / or 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, 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.

For example, in the esterification reaction step, an aromatic dicarboxylic acid and an aliphatic diol are polymerized in the presence of a catalyst containing a titanium compound. In this esterification reaction step, an organic chelate titanium complex having an organic acid as a ligand is used as a catalyst titanium compound, and at least an organic chelate titanium complex, a magnesium compound, and an aromatic ring as a substituent in the step. And a process of adding a pentavalent phosphate ester having no sulfite in this order.

First, an aromatic dicarboxylic acid and an aliphatic diol are mixed with a catalyst containing an organic chelate titanium complex, which is a titanium compound, prior to addition of a magnesium compound and a phosphorus compound. Titanium compounds such as organic chelate titanium complexes have high catalytic activity for esterification reactions, so that esterification reactions can be performed satisfactorily. At this time, the titanium compound may be added to the mixture of the dicarboxylic acid component and the diol component, or after mixing the dicarboxylic acid component (or diol component) and the titanium compound, the diol component (or dicarboxylic acid component) is mixed. May be. 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.

More preferred polyesters are polyethylene terephthalate (PET) and polyethylene-2,6-naphthalate (PEN), and more preferred is PET. Further, PET has a germanium (Ge) compound (Ge-based catalyst), an antimony (Sb) compound (Sb-based catalyst), an aluminum (Al) compound (Al-based catalyst), and a titanium (Ti) compound (Ti-based catalyst) as catalyst components. Those which are polymerized using one or more selected from (catalyst) are preferred, and titanium compounds are more preferred.

The titanium compound has high reaction activity and can lower the polymerization temperature. Therefore, it is possible to suppress the polyester from being thermally decomposed during the polymerization reaction and generating COOH. That is, by using a titanium compound, the amount of terminal carboxylic acid of polyester that causes thermal decomposition can be reduced, and foreign matter formation can be suppressed. By reducing the amount of the terminal carboxylic acid of the polyester, it is possible to suppress thermal decomposition of the polyester film after the production of the polyester film.
Of the titanium compounds, titanium oxide used as a whitening agent cannot provide such an effect.

[Titanium catalyst]
The titanium compound used as the catalyst, that is, the titanium-based catalyst is preferably at least one of organic chelate titanium complexes having an organic acid as a ligand. 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 having good polymerization activity and color tone can be obtained as compared with other titanium compounds. Furthermore, even when a citric acid chelate titanium complex is used, a method of adding at the stage of esterification reaction gives a polyester having better polymerization activity and color tone and less terminal carboxyl groups than when added after the esterification reaction. . In this regard, the titanium-based catalyst also has a catalytic effect on 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 are not hydrolyzed during the esterification reaction process. It is presumed to function effectively as a catalyst.
In general, it is known that hydrolysis resistance deteriorates as the amount of terminal carboxyl groups increases, and the hydrolysis resistance is expected to be improved by decreasing the amount of terminal carboxyl groups by the above addition method. .

As the citrate chelate titanium complex, for example, VERTEC® AC-420 manufactured by Johnson Matthey can be easily obtained as a commercial product.

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 addition to the organic chelate titanium complex, titanium compounds generally include oxides, hydroxides, alkoxides, carboxylates, carbonates, oxalates, and halides. Other titanium compounds may be used in combination with the organic chelate titanium complex as long as the effects of the present invention are not impaired.
Examples of such titanium compounds include tetra-n-propyl titanate, tetra-i-propyl titanate, tetra-n-butyl titanate, tetra-n-butyl titanate tetramer, tetra-t-butyl titanate, tetracyclohexyl titanate, Titanium alkoxide such as tetraphenyl 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 titanium oxalate, potassium titanate, sodium titanate, titanium titanate-aluminum hydroxide mixture, titanium chloride, titanium chloride Down - aluminum chloride mixture, and titanium acetylacetonate.

When the polyester is polymerized, it is preferable to use a titanium compound (including a titanium-based catalyst) in the range of 1 ppm to 50 ppm, more preferably 2 ppm to 30 ppm, and still more preferably 3 ppm to 15 ppm. In this case, the raw material polyester contains 1 ppm or more and 50 ppm or less of titanium element.
If the amount of titanium compound (including titanium-based catalyst) contained in the raw material polyester is less than 1 ppm, the weight average molecular weight (Mw) of the polyester cannot be increased, and thermal decomposition tends to occur, so foreign matter increases in the extruder. It is easy to do and is not preferable. When the amount of the titanium compound (including the titanium-based catalyst) contained in the raw material polyester exceeds 50 ppmm, the titanium compound (including the titanium-based catalyst) becomes a foreign substance, and causes uneven stretching when the polyester sheet is stretched. Absent.

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. An esterification reaction step including at least a step 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, and an ester formed in the esterification reaction step And a polycondensation step in which a polycondensation product is produced by a polycondensation reaction of the chemical reaction product, and is preferably produced by a polyester production method.

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 adding a titanium series. Since the reaction activity of the catalyst is kept moderately high, the electrostatic application characteristics due to magnesium can be imparted, and the decomposition reaction in the polycondensation can be effectively suppressed, resulting in less coloring and high electrostatic application characteristics. A polyester 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, yellowness is reduced as compared with conventional antimony (Sb) catalyst-based polyester, and germanium catalyst system with relatively high transparency. Compared with other polyesters, it is possible to provide polyesters that have a color tone and transparency that are inferior to those of other polyesters and that have excellent heat resistance. Moreover, polyester which has high transparency and few yellowishness is obtained, without using color tone adjusting materials, such as a cobalt compound and a pigment | dye.

This polyester 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 esterification reaction, a process of adding an organic chelate titanium complex which is a titanium compound and a magnesium compound and a pentavalent phosphorus compound as additives in this order is provided. 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 compounds]
As the pentavalent phosphorus compound, at least one pentavalent phosphate having no aromatic ring as a substituent is used. For example, phosphoric acid esters 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], specifically, phosphoric acid Trimethyl and triethyl phosphate are particularly preferable.

The amount of phosphorus compound added 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 or more and 80 ppm or less, and still more preferably 60 ppm or more and 75 ppm or less.

[Magnesium compound]
By including a magnesium compound in the polyester, the electrostatic applicability of the polyester is improved. 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.

As the addition amount of the magnesium compound, in order to impart high electrostatic applicability, the Mg element conversion value is preferably 50 ppm or more, and more preferably 50 ppm or more and 100 ppm or less. 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, the value Z calculated from the following formula (i) for the titanium compound as the catalyst component and the magnesium compound and phosphorus compound as the additive satisfies the following relational expression (ii). Thus, the case where it is added and melt polymerized is particularly preferred. 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 excellent in coloring resistance can be obtained.

In the formula (ii), it is preferable that 1.0 ≦ Z ≦ 4.0 is satisfied and 1.5 ≦ Z ≦ 3 from the viewpoint of further increasing the color tone and the coloration resistance to heat while maintaining the polymerization reactivity. 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 weak acid of 60 ppm to 90 ppm (more preferably 70 ppm to 80 ppm) is added, and after the addition, 60 ppm to 80 ppm (more preferably 65 ppm to 75 ppm). 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 carried out in one stage, the esterification reaction temperature is preferably 230 to 260 ° C, more preferably 240 to 250 ° C.
When the esterification reaction is carried out 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. The temperature of the esterification reaction in the second reaction tank is preferably 230 to 260 ° C., more preferably 245 to 255 ° C., and the pressure is 0.5 to 5.0 kg / 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.

-Polycondensation-
In polycondensation, a polycondensation product is produced by subjecting an esterification reaction product produced by the esterification reaction to a polycondensation reaction. 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 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 100 to 10 torr (13.3). × 10 ⁻³ to 1.3 × 10 ⁻³ MPa), more preferably 50 to 20 torr (6.67 × 10 ⁻³ to 2.67 × 10 ⁻³ MPa). The temperature is 265 to 285 ° C., more preferably 270 to 280 ° C., and the pressure is 20 to 1 torr (2.67 × 10 ⁻³ to 1.33 × 10 ⁻⁴ MPa), more preferably 10 to 3 torr (1. 33 × 10 ⁻³ to 4.0 × 10 ⁻⁴ MPa), 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 10-0.1tor ^{(1.33 × 10 -3 ~ 1.33 ×} 10 -5 MPa), aspect is preferably more preferably ^{5 ~ 0.5torr (6.67 × 10 -4} ~ 6.67 × 10 -5 MPa) .

Additives such as light stabilizers, antioxidants, UV absorbers, flame retardants, lubricants (fine particles), nucleating agents (crystallization agents), crystallization inhibitors, etc. to the polyester synthesized as described above May further be included.

The polyester that is the raw material of the polyester sheet is preferably a solid-phase polymerized pellet.
After polymerization by the esterification reaction, solid phase polymerization is further performed, whereby the moisture content of the polyester film, the crystallinity, the acid value of the polyester, that is, the concentration of the terminal carboxyl group of the polyester (Acid Value; AV, unit: equivalent / T) and intrinsic viscosity (Intrinsic Viscosity; IV, unit: dl / g). In the present specification, “equivalent / ton” represents a molar equivalent per ton.
The intrinsic viscosity (IV) of the polyester is preferably 0.7 or more and 0.9 or less.
When the intrinsic viscosity is 0.7 or more, the molecular motion of the polyester is hindered and it is difficult to crystallize. When the intrinsic viscosity is 0.9 or less, thermal decomposition of the polyester due to shear heat generation in the extruder does not occur too much, Crystallization can be suppressed and the acid value (AV) can be kept low.
IV is more preferably 0.75 or more and 0.85 or less.

In particular, in the esterification reaction, a Ti catalyst is used, and further, solid-phase polymerization is performed so that the intrinsic viscosity (IV) of the polyester is 0.7 or more and 0.9 or less. In the cooling step, it is easy to suppress the crystallization of the polyester.
Therefore, the polyester that is a raw material of the polyester sheet preferably has an intrinsic viscosity of 0.7 or more and 0.9 or less.

The intrinsic viscosity (IV) is 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 ) (η _sp = η _r −1). It is a value obtained by extrapolating the value divided by the density to a state where the density is zero. IV is obtained from a solution viscosity at 25 ° C. by using a Ubbelohde viscometer, dissolving polyester in a 1,1,2,2-tetrachloroethane / phenol (= 2/3 [mass ratio]) mixed solvent.

In the solid phase polymerization of polyester, a polyester obtained by the esterification reaction described above or a commercially available polyester in the form of a small piece such as a pellet may be used as a starting material.
The solid phase polymerization of polyester may be a continuous method (a method in which a tower is filled with a resin, and this is slowly heated for a predetermined period of time while being heated and then sequentially fed out), or a batch method (a resin is placed in a container). Or a method of heating for a predetermined time).
The solid phase polymerization is preferably performed in a vacuum or a nitrogen stream.

The temperature of the solid phase polymerization is preferably 170 ° C. or higher and 240 ° C. or lower, more preferably 180 ° C. or higher and 230 ° C. or lower, and further preferably 190 ° C. or higher and 220 ° C. or lower. When the temperature is within the above range, it is preferable in that the acid value (AV) of the polyester is further reduced. The solid phase polymerization time is preferably 5 hours to 100 hours, more preferably 10 hours to 75 hours, and still more preferably 15 hours to 50 hours. It is preferable that the time is within the above range in that the acid value (AV) and intrinsic viscosity (IV) of the polyester can be easily controlled within the preferable ranges of the present invention. The solid phase polymerization is preferably performed in a vacuum or in a nitrogen atmosphere.

[Stretching process]
It is preferable that the manufacturing method of the polyester film of this invention includes the extending process of extending | stretching the polyester sheet obtained by the extrusion process other than the already described extrusion process.
In the present invention, the polyester sheet refers to a polyester molded body obtained from the polyester obtained by the extrusion process, which is the object of stretching. On the other hand, the polyester film refers to a polyester molded body that is a target of collection after the stretching of the polyester sheet is completed.

The thickness of the polyester sheet that has not been stretched is preferably 3 mm to 5 mm, and the thickness of the polyester film that has been stretched is thinner than the polyester sheet (for example, less than 1 mm).

The method for stretching the polyester sheet may be uniaxial stretching or biaxial or multiaxial stretching. Biaxial stretching refers to stretching at least once each in different directions.
From the viewpoint of strength and shape stability of the obtained polyester film, the polyester sheet is stretched in the transport direction (MD), that is, longitudinal stretching, and stretched in the direction (TD) orthogonal to the transport direction, that is, lateral stretching. Axial stretching is preferred.

The biaxial stretching method may be any of a sequential biaxial stretching method in which longitudinal stretching and lateral stretching are separated and a simultaneous biaxial stretching method in which longitudinal stretching and lateral stretching are simultaneously performed.
The longitudinal stretching and the lateral stretching may be independently performed twice or more, and the order of the longitudinal stretching and the lateral stretching is not limited. For example, stretching modes such as longitudinal stretching → transverse stretching, longitudinal stretching → transverse stretching → longitudinal stretching, longitudinal stretching → longitudinal stretching → transverse stretching, transverse stretching → longitudinal stretching can be mentioned. Of these, longitudinal stretching → transverse stretching is preferred.
In addition, about transverse stretch, "the direction (TD) orthogonal to the conveyance direction (MD) of a polyester sheet" means the direction of an angle (90 degrees) perpendicular to the conveyance direction (MD) of polyester, and the conveyance direction of polyester ( MD) and an angle (90 ° ± 5 °) that can be regarded as vertical.

In the longitudinal stretching and lateral stretching, the area stretch ratio of the polyester sheet (the product of the stretch ratios) is preferably 6 to 18 times, more preferably 8 to 16 times the area of the polyester sheet before stretching, More preferably, it is 10 to 15 times.
In longitudinal stretching and lateral stretching, the temperature during stretching of the polyester sheet (stretching temperature) is preferably Tg−20 ° C. or more and Tg + 50 ° C., more preferably Tg−, when the glass transition temperature of the polyester sheet is Tg. It is 10 degreeC or more and Tg + 40 degrees C or less, More preferably, it is Tg or more and Tg + 30 degreeC.

In stretching the polyester sheet, it is preferable to perform heat setting after biaxial stretching by a combination of longitudinal stretching and lateral stretching. The heat setting temperature is preferably 160 ° C to 250 ° C, more preferably 180 ° C to 240 ° C, and further preferably 200 ° C to 240 ° C.
After heat setting, it is preferable to apply relaxation of 1% to 20%, more preferably 3% to 15%, and still more preferably 4% to 10% in at least one direction of longitudinal stretching and lateral stretching.

In the stretching process, as a means for heating the polyester sheet, when stretching using a roll such as a nip roll, a polyester sheet in contact with the roll is provided by providing a pipe through which a heater or a hot solvent can flow inside the roll. Can be heated. Even when a roll is not used, the polyester sheet can be heated by blowing warm air on the polyester sheet, contacting the polyester sheet with a heat source such as a heater, or passing the vicinity of the heat source.

The conditions common to both the longitudinal stretching and the lateral stretching have been described above.
Next, details of stretching conditions in longitudinal stretching and lateral stretching will be described.

-Longitudinal stretching-
The longitudinal stretching of the polyester sheet can be performed, for example, by using two or more pairs of nip rolls that are sandwiched between the polyester sheets and arranged in the conveying direction of the polyester sheet.
Specifically, for example, when a pair of nip rolls A is installed on the upstream side in the conveyance direction of the polyester sheet and a pair of nip rolls B is installed on the downstream side, when the polyester sheet is conveyed, the rotational speed of the nip roll B on the downstream side Is made faster than the rotational speed of the nip roll A on the upstream side, whereby the polyester sheet is stretched in the conveying direction (MD).
Two or more pairs of nip rolls may be installed independently on the upstream side and the downstream side, respectively.
Moreover, you may perform the longitudinal stretch of a polyester sheet using the longitudinal stretch apparatus provided with the said nip roll.

(Conveying speed of polyester sheet)
In the present invention, in order to suppress stretching unevenness, the polyester sheet transport speed when starting to stretch the polyester sheet is 30 m / min to 100 m / min, and the transport speed is 0.01% to 1%. % Variation is preferred.
In longitudinal stretching, when the conveyance speed is changed by 0.01% to 1%, the stretching stress varies, and the stretching stress increases or decreases. When the stretching stress increases, stress concentration occurs around the foreign material (residues of pyrolysis components generated in the extruder or grown spherulites), and the vicinity of the foreign material is also stretched to reduce stretching unevenness.
The fluctuation amount of the conveyance speed is more preferably 0.05% to 0.7%, and further preferably 0.1% to 0.5%.

For example, in a longitudinal stretching apparatus in which a pair of nip rolls A is installed on the upstream side in the conveyance direction of the polyester sheet and a pair of nip rolls B is installed on the downstream side, driving for driving the nip roll B occurs. This can be achieved by giving a variation to the current value of the motor.
In addition, the fluctuation amount of the conveyance speed is expressed as a percentage by dividing the difference between the maximum speed and the minimum speed per minute by the average value. The frequency of occurrence of fluctuations that vary the transport speed [times / second] is preferably in the range of 0.01 to 50, and more preferably 0.1 to 10.

Further, in the waveform representing the conveyance speed with respect to time, the half width of the peak representing the conveyance speed that is ± 0.1% or more of the average value of the conveyance speed is ¼ or less of the reciprocal of the average value of the conveyance speed. Further, it is preferable to give a variation to the conveyance speed.
The “waveform representing the conveyance speed with respect to time” in the present invention may be considered in the same manner as the “waveform representing the screw rotation speed N with respect to time” described with reference to FIGS. 4 and 5. That is, with the horizontal axis representing time and the vertical axis representing the conveyance speed in longitudinal stretching, the locus when plotting the conveyance speed against time is a spike-like shape in which peaks appear irregularly as shown in FIG. 4 or FIG. A waveform is preferred. In the waveform representing the conveyance speed with respect to time, the peak indicates a maximum waveform or a minimum waveform having a conveyance speed that is greater than ± 0.1% of the average value of the conveyance speed.

A maximal waveform having a conveyance speed that is greater than + 0.1% of the average value of the conveyance speed indicates a fluctuation in which the conveyance speed accelerates from the average value of the conveyance speed and decelerates from the maximum value. A minimal waveform having a conveyance speed that is greater than or equal to -0.1% of the value indicates a fluctuation in which the conveyance speed is decelerated from the average value of the conveyance speed and accelerated from the minimum value.

In such a spike-like waveform, it is preferable to increase or decrease the conveyance speed in the longitudinal stretching so that the half width of the peak is ¼ or less of the reciprocal of the average value of the conveyance speed. In other words, the “reciprocal of the conveyance speed [m / min]” is the time [minute] required to convey the polyester sheet by 1 m. Therefore, when the time [minute] required to convey the polyester sheet 1 m is t, and the half-value width of the maximum peak or the minimum peak in the waveform representing the conveyance speed with respect to time is Δt, “the half-value width Δt is the average of the conveyance speed. “Less than 1/4 of the reciprocal of the value” can be approximated as Δt ≦ t × 1/4, that is, Δt / t ≦ 1/4.
In the waveform representing the conveyance speed with respect to time, the half width of the peak is more preferably 1/10 or less of the reciprocal of the average value of the conveyance speed.

In the waveform representing the conveyance speed with respect to time, when a variation in which the maximum waveform or the minimum waveform is made continuous is given, the sum of the half-value widths Δt of the continuous maximum waveform or the minimum waveform (ΣΔt) is the reciprocal of the average value of the conveyance speed. What is necessary is just to become 1/4 or less.

As described above, it is preferable that the unevenness in stretching can be more efficiently suppressed by intermittently changing the conveyance speed.

Further, “when starting to stretch the polyester sheet” refers to when a tension for stretching is applied to the polyester sheet.
Therefore, specifically, “the conveyance speed of the polyester sheet when starting the stretching of the polyester sheet” is, for example, a pair of nip rolls A on the upstream side in the conveyance direction of the polyester sheet and a pair of nip rolls on the downstream side. In the longitudinal stretching apparatus in which B is installed, it refers to the conveyance speed when the polyester sheet passes through the nip roll A installed on the upstream side in the conveyance direction.
In the longitudinal stretching, the polyester sheet transport speed when starting the stretching of the polyester sheet is 30 m / min to 100 m / min, so that the effect due to the variation of the stretching stress can be easily obtained. The conveying speed of the polyester sheet when starting the stretching of the polyester sheet is more preferably 35 m / min to 80 m / min, and further preferably 40 m / min to 70 m / min.

(Temperature distribution of polyester sheet)
In the longitudinal stretching, it is preferable to give a temperature distribution of 0.1 ° C. to 30 ° C. in the thickness direction of the polyester sheet to the polyester sheet when stretching of the polyester sheet is started.
The temperature distribution in the thickness direction of the polyester sheet is such that the temperature is high or low from one side of the polyester sheet to the other, or the temperature is high or low from the inside to the surface of the polyester sheet. The state that has become.
Further, “there is a temperature distribution” means a state in which the polyester sheet has a so-called temperature unevenness in which two or more different temperatures are present on the surface and inside. Further, “temperature distribution from 0.1 ° C. to 30 ° C.” means that the difference between the lowest temperature and the highest temperature on the surface and inside of the polyester sheet is 0.1 ° C. to 30 ° C.

Among the above, the temperature distribution in the thickness direction of the polyester sheet is preferably in a state where the inside is at a lower temperature than the surface of the polyester sheet. That is, it is preferable to have a temperature distribution in which the temperature increases from the inside to the surface of the polyester sheet.
This is because the foreign material remaining in the polyester as a thermal decomposition component of the melt in the extruder and the spherulite (foreign material) which has grown in the spherulite and remained in the polyester are separated from the polyester sheet by a cast drum or a peeling roll. Since it tends to be pushed into the inside, it often exists inside the thickness direction of the polyester sheet.

Here, by making the temperature inside the polyester sheet smaller than the temperature of the surface of the polyester sheet, the stretching stress increases, and stretching unevenness in the vicinity of the foreign matter can be reduced. Giving such a temperature distribution in the thickness direction of the polyester sheet can be achieved by shortening the contact time of the polyester sheet with a heating roll (for example, a nip roll having a heater). More specifically, the polyester sheet conveyance speed is preferably set to the above speed (30 m / min to 100 m / min).
The temperature distribution in the thickness direction of the polyester sheet is more preferably 0.5 ° C. to 25 ° C., and further preferably 1 ° C. to 20 ° C.

Furthermore, the thickness of the polyester sheet is preferably 300 μm or more and 6000 μm, more preferably 500 μm or more and 5000 μm or less, and still more preferably 1000 μm or more and 4000 μm or less. Thereby, the spreading | diffusion of the heat | fever to the inside of a polyester sheet can be suppressed, and the said temperature distribution can be achieved.
By setting it as the said range, it becomes easy to give temperature distribution to the thickness direction of the polyester sheet in longitudinal stretch. Furthermore, the increase in the stretching tension accompanying the increase in thickness of the polyester sheet has the effect of further increasing the stretching stress applied to the vicinity of foreign matter that may be present in the polyester sheet and reducing stretching unevenness.

-Transverse stretching-
The lateral stretching of the polyester sheet is performed by widening the polyester sheet in a direction (TD) perpendicular to the conveying direction (MD) of the polyester sheet. In the transverse stretching, generally, both ends of the polyester sheet in the TD direction are gripped by a gripping member and widened.
Further, the lateral stretching of the polyester sheet is performed by using a lateral stretching apparatus or a biaxial stretching machine having a preheating portion, a stretching portion, and a heat treatment portion in this order, and gripping an end portion of the polyester sheet, It is preferable to laterally stretch the polyester sheet while transporting it to the stretching section and the heat treatment section.
First, a biaxial stretching machine will be described.

(Biaxial stretching machine)
FIG. 2 shows an example (top view) of a biaxial stretching machine.
FIG. 2 shows a biaxial stretching machine 200 and a polyester sheet 220 attached to the biaxial stretching machine 200. The biaxial stretching machine 200 includes a pair of

annular rails

21 a and 21 b and is arranged symmetrically with the polyester sheet 220 interposed therebetween.

The biaxial stretching machine 200 includes a preheating unit 22 that preheats the polyester sheet 220 before stretching, a stretching unit 24 that stretches the polyester sheet 220 in the arrow TD direction, which is a direction orthogonal to the arrow MD direction, and after stretching. The heat treatment part 26 heat-treats the polyester film. As a method of heat-treating the stretched polyester film, a heat-fixing process in which the stretched and tensioned polyester film is heated with tension applied, or heat that releases the tension and relaxes the polyester film after the heat-fixing process. Examples include relaxation treatment.

The annular rail 20a includes at least gripping

members

21a, 21b, 21e, and 21f that can move the edge of the annular rail 21a, and the annular rail 21b includes gripping

members

21c, 21d, and 21g that can move the edge of the annular rail 20b. , And 21h. The

grip members

21a, 21b, 21e, and 21f grip one end of the polyester sheet 220 in the TD direction, and the

grip members

21c, 21d, 21g, and 21h are the other end of the polyester sheet 220 in the TD direction. Hold the end. The gripping members 21a to 21h are generally called chucks, clips, and the like.
The gripping

members

21a, 21b, 21e, and 21f move counterclockwise along the edge of the annular rail 20a, and the gripping

members

21c, 21d, 21g, and 21h are clocked along the edge of the annular rail 20b. Move around.

The gripping members 21a to 21d grip the end portion of the polyester sheet 220 in the preheating unit 22, move the edge of the

annular rail

20a or 20b as it is, and proceed to the heat treatment unit 26 where the gripping members 21e to 21h are shown. The gripping members 21a to 21d moved from the preheating unit 22 to the heat treatment unit 26 separate the end of the polyester sheet 220 at the downstream side in the MD direction of the heat treatment unit 26, for example, at positions where the gripping

members

21f and 21h are shown, It advances along the edge of the

annular rail

20a or 20b as it is, and returns to the preheating part 22.
As a result, the polyester sheet 220 moves in the direction of the arrow MD, and is sequentially conveyed to the preheating unit 22, the stretching unit 24, and the heat treatment unit 26.
Although only eight gripping members 21a to 21h are shown for gripping the end of the polyester sheet 220 in the TD direction, the biaxial stretching machine 200 supports 21a to 21h to support the polyester sheet 220. In addition, it has a gripping member (not shown).

In the heat setting treatment, heating (for example, 210 ° C.) is performed while maintaining the tension (for example, tension of 1 kg / m to 10 kg / m) applied to the polyester sheet 220 in the stretching unit 24 to achieve the above-described area stretching ratio. ~ 230 ° C). By this treatment, the crystal of the polyester film can be oriented to give flatness and dimensional stability. If necessary, it can be heated (eg, 210 ° C. to 230 ° C.) while being in the TD direction or MD direction. Thermal relaxation treatment (relaxation treatment) that relaxes 1% to 12% may be performed.
The heat-set polyester film is usually cooled to Tg or less, and the grip portions at both ends of the polyester film are cut and wound into a roll. At this time, it is preferable to perform a treatment that relaxes 1% to 12% in the TD direction and / or MD direction within a temperature range not higher than the final heat setting temperature and not lower than Tg.

The biaxial stretching machine 200 is capable of lateral stretching in which the polyester sheet 220 is stretched in the TD direction in the stretching unit 24. However, the biaxial stretching machine 200 increases the moving speed of the gripping members 21a to 21d, It is possible to extend in the MD direction by increasing the distance between and the distance between the

gripping members

21c and 21d. That is, simultaneous biaxial stretching can be performed using the biaxial stretching machine 200.
Although the transverse stretching apparatus is not shown, it has the same structure as the biaxial stretching machine except that it does not stretch in the MD direction (longitudinal stretching), and a gripping member that grips the polyester sheet, and A rail having a gripping member is provided. It is the same as that of a biaxial stretching machine also about that the horizontal stretching apparatus is comprised at least by the preheating part, the extending | stretching part, and the heat processing part, and its function.
Next, the fluctuation | variation of the conveyance speed of the polyester sheet 220 is demonstrated. Note that the reference numerals in the drawings are omitted.

(Fluctuation of polyester sheet conveyance speed)
As described above, the polyester sheet is conveyed from the preheating portion to the heat treatment portion by moving the edge of the annular rail by the gripping member that holds the end of the polyester sheet in the TD direction. Therefore, the moving speed of the gripping member becomes the conveying speed of the polyester sheet.
In the biaxial stretching machine, when the polyester sheet is gripped by the gripping member and stretched in the TD direction at the stretching section, the polyester sheet conveyance speed (that is, the gripping member moving speed) is 0.1% to 5%. It is preferable to give a variation of%.
If foreign matter remains in the polyester sheet, the portion where the foreign matter exists and the vicinity thereof are difficult to stretch, and as described above, stretching unevenness is likely to occur during stretching. Here, as described above, by varying the conveyance speed of the polyester sheet, stress unevenness is generated during stretching, that is, a large stress is instantaneously generated. Such a large stress promotes stretching in the vicinity of a foreign object that is difficult to stretch, and reduces stretching unevenness. In addition, the fluctuation | variation of the conveyance speed of a polyester sheet divides the difference of the maximum speed and minimum speed of 1 minute by an average value, and was described with the percentage. The frequency of occurrence of fluctuations in the conveyance speed of the polyester sheet [times / second] is preferably in the range of 0.01 to 50, and more preferably 0.1 to 10.
The fluctuation amount of the conveyance speed of the polyester sheet is more preferably 0.3% to 3.5%, and further preferably 0.5% to 2%.

You may perform the manufacturing method of the polyester film of this invention using the biaxial stretching machine which connected the vent type biaxial extruder, the longitudinal stretch apparatus, and the horizontal stretch apparatus in series.
FIG. 3 shows a top view (FIG. 3A) and a side view ((FIG. 3B) of a biaxial stretching machine in which a bent type biaxial extruder, a longitudinal stretching apparatus, and a transverse stretching apparatus are connected in series.
A biaxial stretching machine 300 shown in FIGS. 3A and 3B includes a bent biaxial extruder 30, a longitudinal stretching device 50, a lateral stretching device 60, and a polyester film winder 70 connected in series in this order. Has been.

The vent type biaxial extruder 30 includes at least a hopper 32 and a vent hole 34, and an extrusion die 42 and a cooling device 44 are installed adjacent to the vent type biaxial extruder 30.
The cooling device 44 includes a cast drum.
The longitudinal stretching device 50 is located downstream of the cooling device 44 in the MD direction (arrow direction), and is installed between the cooling device 44 and the lateral stretching device 60.
The transverse stretching device 60 is located downstream of the longitudinal stretching device 50 in the MD direction, and is installed between the longitudinal stretching device 50 and the winder 70. The transverse stretching device 60 includes a preheating unit 62, a stretching unit 64, a heat treatment unit 66, and a cooling unit 68 from the upstream side to the downstream side in the MD direction.
The winding unit 70 is located downstream of the transverse stretching device 60 in the MD direction.
The transverse stretching apparatus 60 shown in FIG. 3 may be replaced with a biaxial stretching machine capable of stretching in the MD direction, such as the biaxial stretching machine 200 shown in FIG.

An outline will be given until the raw material polyester is recovered as a polyester film by the biaxial stretching machine 300.
The raw material polyester put into the hopper 32 is melt-kneaded by a screw (not shown) provided in the vent type twin-screw extruder 30, and then extruded from an extrusion port (not shown) to an extrusion die 42, and a cooling device 44. The polyester sheet is manufactured by being cooled and solidified by a cooling member such as a cast drum provided in the above.
The polyester sheet is conveyed to the longitudinal stretching device 50 and stretched (longitudinal stretching) in the MD direction to become a polyester film. The longitudinally stretched polyester film is subsequently transported to the transverse stretching device 60, heated by the preheating unit 62, widened in the direction perpendicular to the MD direction (TD direction) by the stretching unit 64, and heat set by the heat treatment unit 66. And heat relaxation treatment is performed. Thereafter, the polyester film is cooled in the cooling unit 68 to produce a biaxially stretched polyester film. The produced biaxially stretched polyester film is wound up by the winder 70 and collected.

<Polyester film>
The polyester film of the present invention is a polyester film manufactured by the above-described method for manufacturing a polyester film of the present invention.
It is preferable to produce a polyester film having a thickness of 30 μm to 400 μm by the method for producing a polyester film of the present invention. That is, the thickness after biaxial stretching through longitudinal stretching and lateral stretching is preferably 30 μm to 400 μm.
The thickness of the polyester film is preferably 40 μm to 350 μm, more preferably 50 μm to 300 μm, from the viewpoint of electrical insulation.
The obtained polyester film is suitable for uses such as a solar cell backsheet and a barrier film substrate.

<Back sheet for solar cell>
The above-described polyester film of the present invention is used for the solar cell backsheet of the present invention.
The solar cell backsheet is a back surface protection sheet disposed on the back surface of the solar cell power generation module opposite to the sunlight incident side.
The back sheet for solar cell of the present invention uses the polyester film of the present invention in which stretching unevenness is suppressed. Therefore, the function of the back sheet for solar cells is unlikely to vary depending on the thickness of the sheet, and the function can be expressed without unevenness. In particular, uneven weather resistance is suppressed.

In the application of the solar cell power generation module, the power generation element (solar cell element) connected by the lead wiring for taking out electricity is sealed with a sealing agent such as ethylene / vinyl acetate copolymer system (EVA system) resin, The aspect comprised by sticking together between transparent substrates, such as glass, and the polyester film (back sheet | seat) of this invention is mentioned. Examples of solar cell elements include silicon-based materials such as monocrystalline silicon, polycrystalline silicon, and amorphous silicon, and copper-indium-gallium-selenium, copper-indium-selenium, cadmium-tellurium, gallium-arsenic, etc. III- Various known solar cell elements such as Group V and II-VI 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. “Parts” and “%” are based on mass unless otherwise specified.
The raw material polyesters described below were synthesized, extruded, stretched, etc. to produce polyester films described in Tables 1 to 5 below (Examples 1 to 88 and Comparative Examples 1 to 8).

<Synthesis of raw material polyester>
[Raw material polyester 1-Titanium catalyst (Ti catalyst) used]
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, and polyester (Ti catalyst) by a continuous polymerization apparatus. System PET) was obtained.

(1) Esterification reaction In the first esterification reaction tank, 4.7 tons of high-purity terephthalic acid and 1.8 tons of ethylene glycol were mixed over 90 minutes to form a slurry. 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 is continuously supplied, and the average residence time is maintained at 250 ° C. with stirring in the reaction vessel. The reaction was carried out for about 4.3 hours. At this time, the citric acid chelate titanium complex was continuously added so that the amount of Ti added was 9 ppm in terms of element. At this time, the acid value of the obtained oligomer was 600 equivalent / ton.

The 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 equivalents / ton. The inside of the second esterification reaction tank is partitioned into three zones, and an ethylene glycol solution of magnesium acetate is continuously supplied from the second zone so that the amount of Mg added is 75 ppm in terms of element, From the third zone, an ethylene glycol solution of trimethyl phosphate was continuously supplied so that the added amount of P was 65 ppm in terms of element.

(2) the polycondensation reaction above-obtained esterification reaction product supplied to the first polycondensation reaction vessel continuously stirring, the reaction temperature 270 ° C., the reaction vessel pressure 20 torr (2.67 × 10 ^{- 3} MPa) and polycondensation with an average residence time of about 1.8 hours.

Further, it 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 5 torr (6.67 × 10 ⁻⁴ MPa), and the residence time was about 1.2 hours. The reaction (polycondensation) was performed under the conditions.

Subsequently, it was further transferred to the third triple condensation reaction tank, in which the temperature in the reaction tank was 278 ° C., the pressure in the reaction tank was 1.5 torr (2.0 × 10 ⁻⁴ MPa), and the residence time was 1.5 hours. The reaction product 1 (polyethylene terephthalate (PET)) was obtained by reaction (polycondensation) under the following conditions.

The obtained reaction product 1 was measured using a high resolution high frequency inductively coupled plasma-mass spectrometry (HR-ICP-MS; AttoM manufactured by SII Nanotechnology) as shown below. As a result, Ti = 9 ppm, Mg = It was 75 ppm and P = 60 ppm. P is slightly reduced with respect to the initial addition amount, but is estimated to have volatilized during the polymerization process.
The obtained polymer had IV = 0.65, terminal carboxyl group concentration AV = 22 eq / ton, melting point = 257 ° C., and solution haze = 0.3%.

-Solid state polymerization-
Further, the reaction product 1 obtained as described above was subjected to solid phase polymerization by a batch method. That is, after putting the reaction product 1 into a container, it was subjected to solid phase polymerization under the following conditions while stirring under vacuum.
After precrystallization at 150 ° C., a solid state polymerization reaction was performed at 190 ° C. for 30 hours.
The obtained raw material polyester 1 had an intrinsic viscosity IV = 0.78 and a terminal carboxyl group concentration AV = 15 equivalents / ton.

[Using raw material polyester 2-antimony catalyst (Sb catalyst)]
Polymerization was carried out by changing the amount of Ti catalyst (titanium alkoxide compound) to be added by the method shown below, thereby obtaining raw material polyesters containing different amounts of antimony (Sb) and different amounts of titanium (Ti). A specific method is as follows.
After transesterification of 100 tons of dimethyl terephthalate and 70 tons of ethylene glycol using calcium acetate monohydrate and magnesium acetate tetrahydrate as a transesterification catalyst according to a conventional method, trimethyl phosphate was added, The transesterification reaction was substantially terminated. Further, titanium tetrabutoxide and antimony trioxide were added, and a polycondensation reaction was performed according to a conventional method under high temperature and high vacuum to obtain a reaction product 2.
The obtained reaction product 2 was measured as described below using high-resolution high frequency inductively coupled plasma-mass spectrometry (HR-ICP-MS; AttoM manufactured by SII Nanotechnology). What was carried out in this way was Examples 33, 34, 78, 79, and 80 in the table, and Examples 33, 78, 79, and 80 all had Ti = 0 ppm and Sb = 9 ppm. Example 34 was prepared so that Ti = 1 ppm and Sb = 9 ppm.
Next, the reaction product 2 was put into a container, subjected to a precrystallization treatment at 150 ° C., and then subjected to a solid-phase polymerization reaction at 190 ° C. for 30 hours while being vacuumed and stirred, so that an intrinsic viscosity IV = 0.78, A raw material polyester 2 having a terminal carboxyl concentration AV = 27 equivalents / ton was obtained.

<Preparation of recycled polyester>
A recycled polyester 1 was prepared by regenerating a used resin of a polyester produced using a Ti catalyst. Moreover, the reproduction | regeneration polyester 2 which reproduced | regenerated the used resin of the polyester manufactured using Sb catalyst was prepared.

<Preparation of pellets and powder>
-pellet-
The obtained raw material polyester 1 was melted, discharged into cold water in a strand form, and immediately cut to prepare cylindrical pellets <cross section: diameter 3 mm, length: 5 mm>. Similarly, for the raw material polyester 2, cylindrical pellets <cross-section: diameter 3 mm, length: 5 mm> were prepared.
Moreover, also about the reproduction | regeneration polyester 1 and the reproduction | regeneration polyester 2, the cylindrical pellet <cross section: diameter 3mm, length: 5mm> was produced.

-powder-
The raw material polyester 1 pellets were placed in a Henschel mixer and crushed by operating at 300 rpm at room temperature. This was passed through a 30-mesh sieve and a 300-mesh sieve, and the remaining polyester was used as a powder.
The raw material polyester 2, regenerated polyester 1 and regenerated polyester 2 were also crushed by the same method and sieved to obtain a powder.

<Manufacture of polyester sheet>
-Extrusion process-
The raw material polyester and recycled polyester were mixed and introduced into the extruder. At this time, the amount of the recycled polyester was adjusted to be 30% with respect to the total mass of the raw material polyester. The raw material polyester and the recycled polyester were used in combination with the same catalyst type. That is, raw material polyester 1 and regenerated polyester 1 were combined, and raw material polyester 2 and regenerated polyester 2 were used in combination.

Further, powders having amounts shown in Tables 1 to 5 were mixed with the total mass of the raw material polyester pellets. At this time, the ratio of the raw material polyester and the regenerated polyester in the powder was adjusted so that the amount of the regenerated polyester powder was 30% with respect to the total mass of the raw material polyester powder.

As an extruder, a vent type twin-screw extruder having the configuration shown in FIG. 1 was prepared, and the pellets and powder prepared as described above were put into a hopper of the extruder.
The amount of titanium-based catalyst contained in the raw material polyester charged into the extruder is shown in “Raw material polyester” and “Ti-based catalyst” in Tables 1 to 5. Those having a catalyst amount of 0 ppm are raw material polyesters of an antimony catalyst system.
The amount of the catalyst was obtained by dissolving the raw material polyester in HFIP (hexafluoroisopropanol) so as to have a concentration of 5%, and further centrifuging at 1000 rpm. The amount of Ti was measured by atomic absorption spectrometry using the obtained supernatant. By this centrifuge treatment, the solid matter of TiO ₂ which is a titanium compound was removed, and only the titanium catalyst was measured.

Tables 1 to 5 show the cylinder inner diameter D of the extruder, the extrusion amount Q per unit time, and the screw rotation speed N. However, screw rotation speed N is an average value in 10 minutes. (Q / N) / (D ^2.8 × 10 ⁻⁶ ) obtained from these are also shown in Tables 1 to 5. The polyester charged in the extruder was extruded at 280 ° C., the temperature at the center of the cylinder was raised to 300 ° C., held for the time indicated in the “heating conditions” column of Tables 1 to 5, and then the heat was removed. The temperature was lowered to ° C. At this time, the screw rotation speed N was given a fluctuation of the magnitude shown in “N fluctuation” and “variation amount” in Tables 1 to 5. The fluctuation of the screw rotation speed N is observed by an oscilloscope that can display a waveform representing the screw rotation speed with respect to time, and the value (Δt / t) of the peak half-value width Δt with respect to the reciprocal t of the screw rotation speed N (average value). This was carried out by adjusting the current of the motor of the screw drive device so that the magnitudes shown in “N fluctuation” and “Δt / t” in Tables 1 to 5 were obtained.
In addition, the vent hole of the extruder was measured from the inlet side of the cylinder and installed at a position of 1/3 of the total length of the cylinder.
A gear pump, a filter, and an extrusion die were connected in this order to the exit (extrusion port) of the extruder. These temperatures were set at 280 ° C.

-cast-
The polyester extruded from the die was cooled and solidified as a sheet on a 10 ° C. cast drum. At this time, an electrostatic application method was used. In the first half of the cast drum, the extruded polyester was cooled by blowing air at 20 ° C. at a wind speed of 50 m / sec. When the cast drum was turned 3/4, the polyester sheet was peeled off to obtain a polyester sheet.
At this time, thickness fluctuation was given to MD direction of a polyester sheet by the fluctuation | variation of the screw speed N of an extruder, and thickness fluctuation | variation was provided to TD direction by giving a vibration to an extrusion die.

Here, the thickness variation in the TD direction is determined by measuring the thickness of the portion (80% of the total width) excluding the region of 10% of the total length in the TD direction (the width of the polyester sheet) from both ends of the polyester sheet in the TD direction. The difference between the thickness and the minimum thickness is divided by the average value and expressed as a percentage.
On the other hand, the thickness variation in the MD direction refers to a value obtained by measuring the thickness over 3 m at the center in the TD direction (width direction), dividing the difference between the maximum thickness and the minimum thickness by the average value, and displaying the percentage. These average values [(“average value of thickness variation in TD direction” + “average value of thickness variation in MD direction”) / 2] are defined as thickness variations and are shown in Tables 1 to 5.

-Stretching process-
The obtained polyester sheet (unstretched polyester sheet) was biaxially stretched by performing longitudinal stretching and lateral stretching in this order. Prior to the longitudinal stretching, 1 cm squares were formed on the surface of the polyester sheet. The grids were printed on a region having a length of 0.2 m in the MD direction excluding a 10% region from both ends in the TD direction of the polyester sheet.

1) Longitudinal Stretching The polyester sheet was stretched by passing it between two pairs of nip rolls so that the rotational speed of the nip roll on the downstream side in the MD direction was faster than the rotational speed of the nip roll on the upstream side. It should be noted that the longitudinal draw ratio was 3.4 times for all levels.
At this time, the polyester sheet is transported at the transport speeds indicated by “longitudinal stretching” and “conveyance speed” in Tables 1 to 5, and is indicated by “longitudinal stretching”, “conveyance speed fluctuation”, and “variation amount” in Tables 1 to 5. The transfer speed was changed by the amount of change. The conveyance speeds shown in Tables 1 to 5 represent average values of speeds when the polyester sheet passes through the nip roll on the upstream side in the MD direction. The fluctuation of the conveyance speed is observed with an oscilloscope capable of displaying a waveform representing the conveyance speed with respect to time. It was carried out by adjusting the current of the drive motor that drives the nip roll on the downstream side in the MD direction so as to have the sizes indicated by “longitudinal stretching”, “conveyance speed fluctuation”, and “Δt / t”.

Further, before longitudinal stretching, the polyester sheet was heated to Tg + 5 ° C. to give the temperature distributions shown in Tables 1 to 5 (temperature distribution in the thickness direction). Tg is the glass transition temperature of the polyester sheet.
At this time, the temperature distribution was determined by measuring the temperatures of the following three points (a) to (c) for the polyester sheet immediately before the polyester sheet during longitudinal stretching passes through the nip roll on the downstream side. The difference between the temperature and the average of the temperature in (c) and the temperature in (a) was determined to obtain a temperature distribution. In addition, these temperature measurement was measured in the center part of the width direction (TD direction) of a polyester sheet.

(A) to (c) The position at which the temperature was measured and the measuring method (a) The temperature at the center of the polyester sheet in the thickness direction The temperature was measured with a thermocouple embedded in the polyester sheet.
(B) One surface of the polyester sheet surface It measured with the thermocouple affixed on one surface of the polyester sheet surface.
(C) The other surface of the polyester sheet surface It measured with the thermocouple affixed on the other surface of the polyester sheet surface.

2) Transverse stretching and winding With respect to the uniaxial polyester film obtained by longitudinal stretching, the biaxial stretching machine having the configuration shown in FIG. Stretched. Tg is the glass transition temperature of the polyester film.
In the transverse stretching, the moving speed of the chuck (gripping member) that grips both ends of the uniaxially stretched polyester film in the TD direction is changed to change the transport speed of the uniaxially stretched polyester film to “Transverse Stretching” in Tables 1 to 5. The fluctuation amount indicated by “Variation speed fluctuation” and “Variation amount” was given. At this time, the fluctuation of the conveyance speed is observed with an oscilloscope capable of displaying a waveform representing the conveyance speed with respect to time, and the value (Δt / t) with respect to the reciprocal t of the average value of the conveyance speed of the peak half-value width Δt is expressed in Table 1. This was carried out by adjusting the current of the drive motor that moves the chuck so that the magnitudes shown in “lateral stretching”, “conveyance speed fluctuation”, and “Δt / t” in Table 5 were obtained.

Next, after heat-fixing treatment at 230 ° C. for 30 seconds in the heat treatment part, heat relaxation treatment is carried out at 220 ° C. in the width direction (TD direction) and the longitudinal direction (MD direction) by 5% each. A biaxially stretched polyester film was obtained.
Thereafter, both ends of the biaxially stretched polyester film were trimmed, and the biaxially stretched polyester film was removed from the chuck. Further, the both sides of the biaxially stretched polyester film were subjected to thicknessing (knurling), and the biaxially stretched polyester film was wound up.
The width (total length in the TD direction) of the biaxially stretched polyester film at this time was 3.5 m, and the thickness was the thickness described in the “Biaxially stretched film” and “Thickness” columns of Tables 1 to 5. This was wound up 3000 m long.

<Evaluation of biaxially stretched polyester film>
From the area of the mesh on the surface of the biaxially stretched polyester film produced through the extrusion process and the stretching process, the degree of stretching unevenness was evaluated and listed in Tables 1 to 5.
Specifically, the vertical and horizontal lengths of the meshes on the surface of the biaxially stretched polyester film were measured and multiplied to obtain the area of each mesh. The average area of all the obtained squares was calculated, and the number of squares (referred to as irregular squares) whose areas differed by 5% or more from the average area (larger or smaller than the average area) was counted. The number of variant cells was divided by the number of all cells and expressed as a percentage. Stretching unevenness was evaluated based on the size of the ratio of irregular shaped meshes expressed as a percentage.
The allowable range is that the ratio of irregular meshes is 30% or less.

<Confirmation of foreign matter remaining on polyester sheet>
The polyester sheet peeled off from the cast drum was collected, and the presence or absence of foreign matter in the polyester sheet before longitudinal and lateral stretching was confirmed.
Specifically, the polyester sheet is cut into 20 cm × 20 cm, the obtained sample is sandwiched between two polarizing plates, the polarizing axes are observed in a parallel arrangement and an orthogonal arrangement, and each is observed with a magnifying glass 5 times, and the location of the foreign matter Marked. The marked locations were counted and the average value per cm ² was calculated.
The evaluation results are shown in the “cast” and “foreign matter” columns of Tables 1 to 5. The allowable range is 15 pieces / cm ² or less.

As can be seen from Tables 1 to 5, the polyester sheet of the example has a small amount of foreign matter remaining compared to the comparative example. Therefore, it is considered that the amount of foreign matter in the polyester was reduced and the foreign matter was eliminated by the extrusion process of the raw material polyester in the present invention. Moreover, it turns out that the biaxially stretched polyester film of an Example has a small ratio (30% or less) of a deformed mesh compared with a comparative example, and the stretching nonuniformity is suppressed. This is because the polyester sheet before stretching contains almost no foreign matter that causes stretching unevenness, and further, by imparting a temperature distribution to the polyester sheet or by varying the transport speed of the polyester sheet in longitudinal stretching or lateral stretching. This is probably because the portion where the foreign matter exists could be stretched.
The disclosure of Japanese Patent Application No. 2011-015656 filed on Jan. 27, 2011 is incorporated herein by reference in its entirety.
All documents, patent applications, and technical standards mentioned in this specification are to the same extent as if each individual document, patent application, and technical standard were specifically and individually described to be incorporated by reference, Incorporated herein by reference.

Claims

The raw material polyester is supplied to a vent type twin-screw extruder having a cylinder inner diameter D of 140 mm or more and 300 mm or less, and the cylinder inner diameter D, the extrusion amount Q (kg / hr.) Per unit time, and the screw rotation speed N (rpm And an extrusion step of melt-extruding the polyester sheet by imparting a variation of 0.01% to 5% to the screw rotational speed N under the conditions satisfying the following formula (I): A method for producing a polyester film comprising a cooling and solidifying step of cooling and solidifying.
In the waveform representing the screw rotation speed N with respect to time, the half width of the peak representing the rotation speed that is ± 0.1% to ± 3% of the average value of the screw rotation speed N is the average of the screw rotation speed N The method for producing a polyester film according to claim 1, which is 1/100 or more and 1/4 or less of the reciprocal of the value.
The method for producing a polyester film according to claim 1 or 2, wherein the raw material polyester includes 0.01% by mass to 5% by mass of polyester powder based on the total mass of the polyester pellets and the polyester pellets.
The method for producing a polyester film according to any one of claims 1 to 3, wherein the extrusion step further gives a thickness variation of 1% to 30% to the melt-extruded polyester sheet.
Furthermore, it includes a stretching step of transporting the melt-extruded polyester sheet to obtain a polyester film by longitudinal stretching and lateral stretching,
In the longitudinal stretching, when the polyester sheet starts to be stretched, the transport speed of the polyester sheet is set to 30 m / min to 100 m / min, and the transport speed is varied by 0.01% to 1%. The method for producing a polyester film according to any one of claims 1 to 4, which is carried out.
In the waveform representing the conveyance speed with respect to time, the half width of the peak representing the conveyance speed that is ± 0.1% to ± 1% of the average value of the conveyance speed is 1 / of the reciprocal of the average value of the conveyance speed. It is 100 or more and 1/4 or less, The manufacturing method of the polyester film of Claim 5.
7. The longitudinal stretching is performed by giving a temperature distribution of 0.1 ° C. to 30 ° C. in the thickness direction of the polyester sheet to the polyester sheet when stretching of the polyester sheet is started. Of manufacturing polyester film.
In the transverse stretching, the end of the polyester sheet is gripped, the polyester sheet is widened in a direction orthogonal to the conveying method, and the conveying speed of the polyester sheet varies by 0.1% to 5%. The method for producing a polyester film according to any one of claims 5 to 7, which is carried out by imparting.
In the waveform representing the conveyance speed with respect to time, the half width of the peak representing the conveyance speed that is ± 0.1% to ± 5% of the average value of the conveyance speed is 1 / of the reciprocal of the average value of the conveyance speed. It is 100 or more and 1/4 or less, The manufacturing method of the polyester film of Claim 8.
The method for producing a polyester film according to any one of claims 5 to 9, wherein a thickness of the polyester film after biaxial stretching in which the longitudinal stretching and the lateral stretching are performed is 30 μm to 400 μm.
The method for producing a polyester film according to any one of claims 1 to 10, wherein the raw material polyester contains 1 ppm to 50 ppm of a titanium-based catalyst.
In the extrusion step, the temperature of the raw material polyester in the bent type twin screw extruder is set to 300 ° C. to 350 ° C. for 1 second to 10 minutes, and then the polyester sheet is heated under a temperature condition of 290 ° C. or lower. The method for producing a polyester film according to any one of claims 1 to 11, wherein the polyester film is melt-extruded.
The method for producing a polyester film according to any one of claims 1 to 12, wherein the frequency of occurrence of fluctuations in the screw rotation speed N is 0.01 times / second to 50 times / second.
The method for producing a polyester film according to claim 8, wherein the occurrence frequency of fluctuation in the polyester sheet conveying speed is 0.01 times / second to 50 times / second.
A polyester film produced by the method for producing a polyester film according to any one of claims 1 to 14.
A solar cell backsheet using the polyester film according to claim 15.
The solar cell power generation module containing the laminated body on which the transparent substrate and the solar cell backsheet of Claim 16 were mutually bonded | interposed on both sides of the solar cell element.