WO2012115167A1

WO2012115167A1 - Method for producing polyester film, and polyester film for solar cells

Info

Publication number: WO2012115167A1
Application number: PCT/JP2012/054319
Authority: WO
Inventors: 山田　晃
Original assignee: 富士フイルム株式会社
Priority date: 2011-02-23
Filing date: 2012-02-22
Publication date: 2012-08-30
Also published as: CN103298595B; JP5653951B2; JP2013136223A; CN103298595A

Abstract

Provided is a method for producing polyester film, the method comprising: a step in which polyester resin is fed to a biaxial extruder (100), and extruded with the resin temperature inside the extruder controlled at a maximum value from 295 to 320°C at a position of 40% to 80% of the entire length of the extruder from the upstream end, and the resin temperature at the extruder outlet (14) within the range of 275 to 285°C; and a step in which the molten-extruded polyester resin is formed into a film. The resultant polyester film has high resistance to thermal decomposition, and generates minimal unmelted impurities during molten extrusion.

Description

Method for producing polyester film and polyester film for solar cell

The present invention relates to a method for producing a polyester film and a polyester film for a solar cell.

In recent years, a resin material such as polyester has been used for the back sheet disposed on the side opposite to the sunlight incident side of the solar cell module. Polyester usually has many carboxyl groups and hydroxyl groups on its surface, and tends to undergo hydrolysis in an environment where moisture exists, and tends to deteriorate over time. For this reason, polyesters used in solar cell modules and the like that are constantly exposed to wind and rain, such as outdoors, are required to have reduced hydrolyzability.

In order to impart hydrolysis resistance to the polyester resin, it is conceivable to reduce terminal COOH that becomes a catalyst for the hydrolysis reaction. Since terminal COOH is generated by heating at the time of melting, it is important to alleviate the thermal history at the time of melting when melt-forming with a plasticizing melt extruder. However, if the temperature of the extruder is simply lowered, an unmelted resin is generated due to temperature unevenness, which becomes a foreign substance when the film is formed in the subsequent stretching process, causing breakage.

In relation to the above situation, a technique is disclosed in which the thermal history is alleviated by placing the extruder in a tandem arrangement and cooling the resin with a second-stage extruder (see, for example, JP-A-10-119112). ).
In addition, in order to achieve mass production while suppressing heat generation, a vent type twin screw extruder with an inner diameter of 140 mm or more is used, and the ratio Q / N between the extrusion amount Q per unit time and the screw rotation speed N is constant. A method for producing a polyester sheet that is melt-extruded under the conditions within the above range is disclosed (for example, see Japanese Patent No. 3577178).

An object of the present invention is to provide a method for producing a polyester film having high hydrolysis resistance while suppressing generation of unmelted foreign matters during melt extrusion, and a polyester film for a solar cell produced thereby.

In order to achieve the above object, the following invention is provided.
<1> Polyester resin is supplied to a twin-screw extruder, and the maximum value in the range of 295 ° C. to 320 ° C. at a position where the resin temperature in the extruder is 40% to 80% of the total length of the extruder from the upstream end of the extruder And melt extrusion by controlling the resin temperature at the exit of the extruder to a range of 275 ° C. to 285 ° C .;
Forming the melt-extruded polyester resin into a film;
The manufacturing method of the polyester film which has this.
<2> The method for producing a polyester film according to <1>, wherein the temperature of at least a part of the cylinder on the downstream side of the position where the resin temperature in the extruder reaches the maximum value is lower than the melting point of the polyester resin. .
<3> The method for producing a polyester film according to <2>, wherein the temperature of at least a part of the cylinder on the downstream side of the position where the resin temperature in the extruder reaches the maximum value is controlled by a liquid heat medium.
<4> The method for producing a polyester film according to any one of <1> to <3>, further comprising a step of allowing the melt-extruded polyester resin to pass through a filter through a gear pump.
<5> The method for producing a polyester film according to any one of <1> to <4>, further comprising a step of allowing the melt-extruded polyester resin to pass through a die before the step of forming the film.

<6> The method for producing a polyester film according to any one of <1> to <5>, wherein pellets and fluff are supplied to the extruder as the polyester resin at a mass ratio of the fluff of 60% or less.
<7> The method for producing a polyester film according to any one of <1> to <6>, wherein the raw material of the polyester resin has an intrinsic viscosity in the range of 0.6 to 0.8.
<8> The method for producing a polyester film according to any one of <1> to <7>, wherein a melting point Tm of the polyester resin raw material obtained by differential scanning calorimetry is in a range of 250 ° C. to 260 ° C.
<9> Polyester film in which the amount of terminal COOH of the polyester in the polyester film produced by the method for producing a polyester film according to any one of <1> to <8> is in the range of 2 eq / t to 20 eq / t. .
<10> A polyester film produced by the production method according to any one of <1> to <8>.

According to the present invention, there is provided a method for producing a polyester film having high hydrolysis resistance while suppressing generation of unmelted foreign matter during melt extrusion. Moreover, according to this invention, the polyester film for solar cells suitable for a solar cell backsheet etc. is provided.

It is the schematic which shows the structural example of the twin-screw extruder for enforcing the manufacturing method of the polyester film which concerns on this invention. It is a figure which shows an example of the flow which enforces the manufacturing method of the polyester film which concerns on this invention.

Hereinafter, the manufacturing method of the polyester film of this invention is demonstrated in detail. In the present specification, “to” is used to mean that the numerical values described before and after it are included as a lower limit value and an upper limit value.
The present inventor conducted research to achieve both low-temperature extrusion and uniform melting.In a short time, using a twin-screw extruder, the resin temperature inside the extruder was maximized from the middle front to the latter half of the extruder. After raising the temperature to a specific temperature range above the melting temperature, the resin is cooled to the outlet of the extruder and the resin temperature at the outlet is controlled to a relatively low temperature so that unmelted foreign matter remains in the conventional method. Even at a high discharge temperature, the polyester resin can be uniformly melted and extruded, thereby suppressing the generation of unmelted resin and effectively suppressing the increase in terminal COOH, thereby producing a film having high hydrolysis resistance. Found that can be obtained.

In the method for producing a polyester film of the present invention, a polyester resin is supplied to a twin-screw extruder, and the resin temperature in the extruder is from 295 ° C. to 40% to 80% of the total length of the extruder from the upstream end of the extruder. A step of melt-extrusion having a maximum value in the range of 320 ° C. and controlling the resin temperature at the exit of the extruder to a range of 275 ° C. to 285 ° C., and molding the melt-extruded polyester resin into a film shape And a process.
Hereinafter, each step will be described.

(Melt extrusion process)
In the present invention, the raw material polyester resin is supplied to a twin screw extruder, and the resin temperature in the extruder is in the range of 295 to 320 ° C. at a position of 40% to 80% of the total length of the extruder from the upstream end of the extruder. And the resin temperature at the exit of the extruder is controlled to 275 ° C. to 285 ° C. to perform melt extrusion.
First, the twin screw extruder that can be used in the present invention will be described. FIG. 1 schematically shows an example of the configuration of a twin-screw extruder used in carrying out the method for producing a polyester film according to the present invention. FIG. 2 shows an example of a flow for carrying out the method for producing a polyester film according to the present invention.
The twin screw extruder shown in FIG. 1 is disposed around a cylinder 10 (barrel) having a supply port 12 and an extruder outlet 14, two

screws

20A and 20B rotating in the cylinder 10, and the cylinder 10. Temperature control means 30 for controlling the temperature in the cylinder 10. A raw material supply device 46 is provided in front of the supply port 12. Further, a gear pump 44, a filter 42, and a die 40 are provided at the tip of the extruder outlet 14 as shown in FIG.

-Cylinder The cylinder 10 has a supply port 12 for supplying the raw material resin and an extruder outlet 14 through which the heat-melted resin is extruded.
For the inner wall surface of the cylinder 10, it is necessary to use a material that is excellent in heat resistance, wear resistance, and corrosion resistance and that can ensure friction with the resin. Generally, nitrided steel whose inner surface is nitrided is used, but chromium molybdenum steel, nickel chromium molybdenum steel, and stainless steel can also be nitrided and used. For applications that require wear resistance and corrosion resistance in particular, a bimetallic cylinder in which a corrosion-resistant and wear-resistant material alloy such as nickel, cobalt, chromium or tungsten is lined on the inner wall surface of the cylinder 10 by centrifugal casting. It is effective to use or form a ceramic sprayed coating.

The cylinder 10 is provided with

vents

16A and 16B for drawing a vacuum. By evacuating through the

vents

16A and 16B, volatile components such as moisture in the resin in the cylinder 10 can be efficiently removed. By appropriately arranging the

vents

16A and 16B, raw materials (pellets, powders, flakes, etc.) in an undried state, crushed waste (fluffs) of the film produced during film formation, etc. can be used as raw material resins as they are. .
The

vents

16A and 16B are required to have an appropriate opening area and number of vents in relation to the deaeration efficiency. The twin-screw extruder 100 used in the present invention desirably has one or

more vents

16A and 16B. If the number of the

vents

16A and 16B is too large, there is a concern that the molten resin may overflow from the vent and there is a concern that the staying deterioration foreign matter may increase. Therefore, it is preferable to provide one or two vents.
In addition, if the resin staying on the wall surface near the vent or the deposited volatile component falls into the extruder 100 (cylinder 10), it may be manifested as a foreign substance in the product, so care must be taken. For retention, optimization of the shape of the vent lid and appropriate selection of the upper vent and the side vent are effective, and precipitation of volatile components is generally performed by a method of preventing precipitation by heating the piping or the like.

For example, when polyethylene terephthalate (PET) is extruded, the suppression of hydrolysis, thermal decomposition, and oxidative decomposition has a great influence on the quality of the product (film).
For example, oxidative decomposition can be suppressed by evacuating the resin supply port 12 or performing a nitrogen purge.
Further, by providing the

vents

16A and 16B at a plurality of locations, even when the raw material moisture content is about 2000 ppm, the same extrusion as when the resin dried to 50 ppm or less is extruded on a single axis is possible.
In order to suppress resin decomposition due to shearing heat generation, it is preferable that segments such as kneading are not provided as much as possible within a range in which extrusion and degassing can be compatible.
Further, since the shear heat generation increases as the pressure at the screw outlet (extruder outlet) 14 increases, the pressure at the extruder outlet 14 is as much as possible within a range in which the degassing efficiency and the stability of the extrusion by the

vents

16A and 16B can be secured. It is preferable to make it low.

揮発 Vacuum components such as moisture in the resin in the cylinder can be efficiently removed by evacuating through the

vents

16A and 16B. If the vent pressure is too low, the molten resin may overflow from the cylinder 10, and if the vent pressure is too high, removal of volatile components may be insufficient, and the resulting film may be easily hydrolyzed. From the viewpoint of preventing the molten resin from overflowing the

vents

16A and 16B and selectively removing volatile components, the vent pressure is preferably 0.01 Torr to 5 Torr (1.333 Pa to 666.5 Pa). More preferably, the pressure is set at 01 Torr to 4 Torr (1.333 Pa to 533.2 Pa).

-Biaxial screw-
In the cylinder 10, two screws 20 </ b> A and 20 </ b> B that are rotated by a driving unit 21 including a motor and a gear are provided. As the screw diameter D increases, mass production is possible, but uneven melting tends to occur. The screw diameter D is preferably 30 to 250 mm, more preferably 50 to 200 mm.

The twin screw extruder is roughly divided into a meshing type and a non-meshing type of the two

screws

20A and 20B, and the meshing type has a larger kneading effect than the non-meshing type. In the present invention, any of a meshing type and a non-meshing type may be used, but it is preferable to use a meshing type from the viewpoint of sufficiently kneading the raw material resin and suppressing melting unevenness.
The rotation directions of the two

screws

20A and 20B are also divided into the same direction and different directions, respectively. The different-

direction rotating screws

20A and 20B have a higher kneading effect than the same-direction rotating type, and the same-direction rotating type has a self-cleaning effect, which is effective for preventing retention in the extruder.
Furthermore, the axial direction is also parallel and oblique, and there is also a conical type shape used when applying strong shear.

In the twin screw extruder used in the present invention, screw segments having various shapes can be used. As the shape of the screws 20 </ b> A and 20 </ b> B, for example, a full flight screw provided with a single helical flight 22 having an equal pitch is used.
By using a segment that imparts shear, such as a kneading disk or a rotor, in the heating and melting part, the raw material resin can be more reliably melted. Further, by using a reverse screw or a seal ring, it is possible to dam the resin and form a melt seal when pulling the

vents

16A and 16B. For example, as shown in FIG. 1, kneading parts 24A (plasticizing kneading parts) and 24B (degassing promoting kneading parts) for promoting melting of the raw material resin as described above can be provided in the vicinity of the

vents

16A and 16B. .

In the vicinity of the exit of the extruder 100, a temperature control zone (cooling section) for cooling the molten resin is effective. When the heat transfer efficiency of the cylinder 10 is higher than the shear heat generation, for example, by providing a screw 28 with a short pitch in the temperature control zone (cooling section), the resin moving speed of the wall surface of the cylinder 10 is increased and the temperature control efficiency is increased. Can do.

-Temperature control means-
A temperature control means 30 is provided around the cylinder 10. In the extruder 100 shown in FIG. 1, heating / cooling devices C1 to C9 divided into nine pieces in the longitudinal direction from the raw material supply port 12 to the extruder outlet 14 constitute the temperature control means 30. Thus, the heating / cooling devices C1 to C9 arranged separately around the cylinder 10 are divided into, for example, heating / melting parts C1 to C7 and cooling parts C8 and C9. Each region can be controlled to a desired temperature.

The heating is usually performed using a band heater or a sheathed wire aluminum cast heater, but is not limited thereto, and for example, a heating medium circulating heating method can also be used. On the other hand, air cooling by a blower is generally used for cooling, but there is also a method of flowing water or oil through a pipe (water passage) wound around the cylinder 10.

-Die-
A die 40 for discharging the molten resin extruded from the extruder outlet 14 into a film shape (band shape) is provided at the tip of the extruder outlet 14 of the cylinder 10. Further, a filter 42 is provided between the extruder outlet 14 of the cylinder 10 and the die 40 to prevent unmelted resin and foreign matter from entering the film.

-Gear pump-
In order to improve the thickness accuracy, it is important to reduce the fluctuation of the extrusion amount as much as possible. A gear pump 44 may be provided between the extruder 100 and the die 40 in order to reduce the variation in the extrusion amount as much as possible. By supplying a certain amount of resin from the gear pump 44, the thickness accuracy can be improved. In particular, when using a twin screw extruder, it is preferable to stabilize the extrusion by the gear pump 44 because the pressurization capacity of the extruder itself is low.

By using the gear pump 44, the pressure fluctuation on the secondary side of the gear pump 44 can be reduced to 1/5 or less on the primary side, and the resin pressure fluctuation width can be within ± 1%. As other merits, it is possible to perform filtration with a filter without increasing the pressure at the tip of the screw, so that prevention of an increase in the resin temperature, improvement in transport efficiency, and shortening of the residence time in the extruder can be expected. It is also possible to prevent the amount of resin supplied from the screw from fluctuating with time due to the increase in the filtration pressure of the filter. However, when the gear pump 44 is installed, the length of the equipment becomes longer depending on the equipment selection method, and the residence time of the resin becomes longer, and the shearing stress of the gear pump section may cause the molecular chain to be broken. It is.

If the difference between the primary pressure (input pressure) and the secondary pressure (output pressure) of the gear pump 44 is excessively increased, the load on the gear pump 44 increases and shear heat generation increases. Therefore, the differential pressure during operation is set to 20 MPa or less, preferably 15 MPa, and more preferably 10 MPa or less. In order to make the film thickness uniform, it is also effective to control the screw rotation of the extruder or to use a pressure control valve in order to keep the primary pressure of the gear pump 44 constant.

-Raw resin-
The raw material resin may be selected in consideration of the physical properties required for the finally required polyester film. For example, it is preferable to use a polyester resin having an intrinsic viscosity IV of 0.5 to 0.9. It is more preferable to use a polyester resin having an IV of 0.6 to 0.8. In the extrusion process of the polyester resin, it is easy to generate heat and the terminal COOH tends to increase, but if the low IV polyester resin as described above is used, the raw resin can be sufficiently kneaded and melted in the heating and melting part, Excessive heating can be suppressed in the cooling section, and an increase in terminal COOH can be effectively suppressed. In particular, if IV is 0.6 or more, it is possible to obtain a film having a sufficiently small terminal COOH, and if it is 0.8 or less, excessive heat generation can be suppressed.
The IV of the raw material resin can be adjusted by the polymerization method and polymerization conditions. Specifically, when solid phase polymerization is performed after liquid phase polymerization, a polyester resin having an intrinsic viscosity IV of 0.6 to 0.8 can be obtained by adjusting the processing temperature, processing time, processing atmosphere moisture, and oxygen concentration. it can.
The intrinsic viscosity (IV) is a specific viscosity (η _sp = η _r −1) obtained by subtracting 1 from the ratio η _r (= η / η ₀ ; relative viscosity) of the solution viscosity (η) and the solvent viscosity (η ₀ ). ) Divided by the density is extrapolated to a density zero state. IV was 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.

Further, the raw material resin preferably has a terminal COOH amount (AV) of 20 eq / t (equivalent / ton) or less, and more preferably 15 eq / t or less. If a raw material resin having a small amount of terminal COOH is used, a polyester film having higher hydrolysis resistance can be obtained. However, for example, from the viewpoint of obtaining adhesion with the adherend, the amount of terminal COOH of the raw material resin is desirably 2 eq / t or more. In the present specification, “equivalent / ton (eq / t)” represents a molar equivalent per ton.

The amount of terminal COOH is a value measured by the following method. That is, after dissolving 0.1 g of the raw material resin in 10 ml of benzyl alcohol, chloroform is further added to obtain a mixed solution, and phenol red indicator is added dropwise thereto. This solution is titrated with a standard solution (0.01 N KOH-benzyl alcohol mixed solution), and the amount of terminal carboxyl groups is determined from the amount added.

In addition, when mixing and using several types of resin, the amount of terminal COOH of the said raw material resin represents the quantity in a mixed state. For example, when polyethylene terephthalate (PET) is mixed with one or more of the pellets or fluff which is a pulverized waste of PET film, the total amount of terminal COOH in the pellet, or the amount of terminal COOH in the pellet and the fluff It is the total amount with the amount of terminal COOH.

The melting point Tm of the raw material resin is preferably in the range of 250 ° C. to 260 ° C. The melting point Tm is a value obtained by differential scanning calorimetry. When mixing a plurality of resins, it is preferable that the average melting point is within the above range.

The bulk specific gravity of the raw material resin is preferably in the range of 0.6 to 0.8. When the bulk specific gravity is 0.6 or more, extrusion can be performed more stably. When the bulk specific gravity is 0.8 or less, local heat generation can be effectively suppressed.
The bulk specific gravity of the raw material resin refers to the specific gravity (per unit volume) obtained by dividing the mass of the powder into a predetermined shape by dividing the powder into a predetermined volume in a constant volume container. Mass), the smaller the bulk specific gravity, the larger the bulk.
Among these, the bulk specific gravity of the raw material resin is particularly preferably in the range of 0.7 to 0.75 from the viewpoint that the increase in terminal COOH is further suppressed by suppressing heat generation during extrusion.

The polyester resin constituting the raw material resin can be obtained by subjecting dicarboxylic acid or an ester derivative thereof and a diol compound to an esterification reaction and / or an ester exchange reaction by a known method.
Examples of the dicarboxylic acid or ester derivative thereof include malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecanedioic acid, dimer acid, eicosandioic acid, pimelic acid, azelaic acid, methylmalon. Aliphatic dicarboxylic acids such as acids, ethylmalonic acids, alicyclic dicarboxylic acids such as adamantane dicarboxylic acid, norbornene dicarboxylic acid, cyclohexane dicarboxylic acid, decalin dicarboxylic acid, terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalene Dicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 4,4′-diphenyldicarboxylic acid, 4,4′-diphenyletherdicarboxylic acid, 5-sodium sulfoisophthalate Acid, phenyl Emissions boys carboxylic acid, anthracene dicarboxylic acid, phenanthrene carboxylic, 9,9'-bis (4-carboxyphenyl) a dicarboxylic acid or an ester derivative such as an aromatic dicarboxylic acid such as fluorene acid.

Examples of the diol compound include aliphatic diols such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-butanediol, and 1,3-butanediol. , Cycloaliphatic diols such as cyclohexanedimethanol, spiroglycol, isosorbide, bisphenol A, 1,3-benzenedimethanol, 1,4-benzendimethanol, 9,9'-bis (4-hydroxyphenyl) fluorene And aromatic diols such as.

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.

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

The Ti catalyst has a high reaction activity and can lower the polymerization temperature. Therefore, it is possible to suppress the thermal decomposition of PET and the generation of COOH particularly during the polymerization reaction. In the present invention, it is suitable for adjusting the terminal COOH amount of the polyester film to a range of 30 eq / ton or less.

For the production of Ti catalyst-based PET obtained by polymerization using a Ti-based catalyst, for example, JP 2005-340616 A, JP 2005-239940 A, JP 2004-319444 A, Patent 3436268, The polymerization methods described in Japanese Patent No. 3978666, Japanese Patent No. 3780137, Japanese Patent Application Laid-Open No. 2007-204538, and the like can be used.

Polymerization is preferably performed using a titanium (Ti) -based compound in the range of 1 ppm to 30 ppm, more preferably 2 ppm to 20 ppm, and even more preferably 3 ppm to 15 ppm. In this case, the polyester film produced by the method of the present invention contains 1 ppm or more and 30 ppm or less of titanium.
When the amount of the Ti-based catalyst is 1 ppm or more, preferable IV is obtained, and when it is 30 ppm or less, the terminal COOH can be kept low, which is advantageous in improving the hydrolysis resistance.

Also, as the form of the raw material resin, pellets, fluffs, mixtures thereof and the like can be used, and those in which the mass ratio of the fluff is 60% or less and mixed with the pellets are preferable. By using a mixture of pellets and fluffs in this way, the melting method and heat history of the raw resin can be adjusted. The fluff is, for example, a pulverized product obtained by pulverizing a film that is no longer needed into small pieces (so-called chips) or scrap pieces. Increasing the fluff ratio has a high recycle ratio and can reduce the cost of raw materials. On the other hand, an increase in the fluff ratio gives a bulkiness, and the bulk specific gravity can be lowered as compared with, for example, a pellet alone. As the resin film for obtaining the fluff, a polyester film is preferable, and a polyester film of the same type as the polyester resin in the raw resin is preferable. By setting the fluff ratio to 60% by mass or less, the fluctuation range of the terminal COOH amount of the obtained polyester film can be kept low. Among these, for the same reason, the mass ratio of the fluff is more preferably 10 to 40%, and particularly preferably 20 to 30%.

The fluff size is not limited as long as the bulk change is given, but a fluff thickness of 20 to 5000 μm is preferable. In particular, the fluff thickness is preferably in the range of 100 to 1000 μm, more preferably in the range of 100 to 500 μm, from the viewpoint of preventing the bulk density from becoming too small and reducing the filling rate too much and avoiding insufficient melting.

Further, in terms of further reducing the amount of terminal COOH of the polyester film to be formed, it is preferable that the variation in the size of the fluff is smaller, for example, the variation in the thickness of the fluff is preferably within ± 100%, more preferably It is within ± 50%, and further within ± 10%. In the case of using a fluff, variation in the terminal COOH amount of the obtained polyester film can be suppressed low by suppressing size variation such as thickness.

The bulk specific gravity of the fluff is preferably in the range of 0.3 to 0.7 as long as the bulk specific gravity of the raw material resin satisfies the above range. The bulk specific gravity is synonymous with the bulk specific gravity of the raw material resin described above, and is measured in the same manner as described above.

-Heating and melting-
The cylinder 10 is heated by the temperature control means 30 and the screw is rotated to supply the polyester resin raw material (raw material resin) from the supply port 12. The supply port 12 is preferably cooled to prevent heat transfer of the raw material resin pellets and the like, and to protect the screw drive equipment such as the motor.

The raw material resin supplied into the cylinder is melted not only by heating by the temperature control means 30, but also by heat generated by friction between the resins accompanying rotation of the

screws

20A and 20B, friction between the resin and the

screws

20A and 20B and the cylinder 10, and the like. And gradually moves toward the extruder outlet 14 as the screw rotates.
The raw material resin supplied into the cylinder is heated to a temperature equal to or higher than the melting point Tm (° C.). However, if the resin temperature is too low, melting during melt extrusion may be insufficient and ejection from the die 40 may be difficult. If the resin temperature is too high, the terminal COOH may be remarkably increased due to thermal decomposition, leading to a decrease in hydrolysis resistance.
In the present invention, by adjusting the heating temperature by the temperature control means 30 and the number of rotations of the

screws

20A and 20B, the resin temperature in the extruder is 295 at a position of 40% to 80% of the total length of the extruder from the upstream end of the extruder. Melt extrusion is performed so that the resin temperature at the extruder exit is 275 ° C. to 285 ° C., with a maximum value of ˜320 ° C. The upstream end of the extruder means the root position where the screw groove is located.

If the maximum value of the resin temperature in the twin screw extruder is less than 295 ° C., a part of the molten resin is solidified to generate an unmelted resin, and if it exceeds 320 ° C., the terminal COOH is increased and the hydrolysis resistance is increased. It will drop greatly. From such a viewpoint, in the present invention, the maximum value of the resin temperature in the twin screw extruder is 295 to 320 ° C., preferably 300 to 315 ° C., and more preferably 305 to 310 ° C.

Also, if the maximum value of the resin temperature in the twin screw extruder is at a position less than 40% of the total length of the extruder from the upstream end of the extruder, the heat generation becomes large and it becomes difficult to sufficiently reduce the outlet resin temperature. If it is at a position exceeding 80%, the resin cooling effect due to cooling becomes insufficient. From this point of view, in the present invention, the maximum value of the resin temperature in the twin-screw extruder is 40% to 80% of the total length of the extruder from the upstream end of the extruder, and 45% to 70% of the total length of the extruder. The position is preferably at a position of 50% to 60%.

On the other hand, the resin temperature at the exit of the twin-screw extruder is usually extruded at about 300 ° C. in the conventional general melt extrusion, but is controlled to be 275 ° C. to 285 ° C. in the present invention. If the resin temperature at the exit of the extruder is less than 275 ° C., unmelted foreign matter is generated, and if it exceeds 285 ° C., the terminal COOH increases and the hydrolysis resistance is greatly reduced. From such a viewpoint, in the present invention, the resin temperature at the exit of the extruder is 275 to 285 ° C., preferably 278 to 283 ° C., more preferably 280 to 282 ° C.

As a means for controlling the resin temperature at the exit of the extruder within the range of 275 ° C. to 285 ° C., air cooling may be used, but it is preferable to control the temperature at the exit of the cylinder with a liquid heat medium. For example, in the heating / cooling device C9 arranged near the outlet of the cylinder, a water passage is provided so as to surround the cylinder, and a liquid such as water is passed through the water passage so that the resin temperature at the outlet of the extruder is efficiently increased. It can be lowered and controlled accurately.

It is preferable that the temperature of at least a part of the cylinder on the downstream side of the position where the resin temperature in the extruder reaches the maximum value is lower than the melting point of the polyester resin. If the temperature of at least a part of the cylinder on the downstream side of the position where the resin temperature in the extruder reaches the maximum value is controlled to be less than the melting point of the polyester resin, the resin at the exit of the extruder is efficiently cooled and the resin The temperature can be controlled between 275 ° C. and 285 ° C. However, if the cylinder temperature is too low, the molten resin may be solidified. Therefore, the temperature of the cylinder on the downstream side of the position where the resin temperature in the extruder on the outlet side of the extruder becomes the maximum value is (polyester resin). The melting point of the polyester resin is preferably −150 ° C.) or more, more preferably (the melting point of the polyester resin−100 ° C.) or more.

The work of the screw is transferred to the resin as frictional heat and is greatly related to the resin temperature. In the present invention, when the extrusion amount (kg / h) is Q and the heat capacity (J / kgK) of the polyester resin is Cp, the following relational expression (1) is satisfied with respect to the heat exchange amount Epoly of the polyester resin. It is preferable.
Epoly + 20QCp <Esp <Epoly + 50QCp (1)
In addition, the specific power of the extruder with respect to the polyester resin can be calculated from the screw current and the voltage as the work amount of the screw.
The heat exchange amount Epoly (J / s) of the polyester resin is calculated by the following formula.
Epoly = QCp (Tout−Tin) + QE
(Q: resin discharge rate (kg / s), Cp: resin heat capacity (J / kg ° C.), Tout: extruder exit resin temperature (° C.), Tin: raw material temperature (° C.), E: latent heat of fusion (J / Kg))

Theoretically, the polyester resin melts by giving the heat exchange amount Epoly of the polyester resin, but the viewpoint of reliably suppressing the increase in the terminal COOH while reliably suppressing the remaining of the unmelted resin and the solidification of the molten resin. Therefore, it is preferable to add the heat amount (work amount) to the heat exchange amount of the polyester resin within a certain range.
If the specific power Esp of the extruder with respect to the polyester resin is larger than (Epoly + 20QCp), the remaining of the unmelted resin and the solidification of the molten resin can be suppressed, while if smaller than (Epoly + 50QCp), the increase in the terminal COOH is suppressed. can do. From this point of view, the specific power Esp of the extruder with respect to the polyester resin more preferably satisfies the relationship of the following formula (2), and more preferably satisfies the relationship of the formula (3).
Epoly + 25QCp <Esp <Epoly + 40QCp (2)
Epoly + 25QCp <Esp <Epoly + 35QCp (3)

In the present invention, it is preferable that the temperature-induced crystallization temperature Tc (° C.) of the water-cooled strand after the polyester resin is melt-extruded with a twin-screw extruder is 130 <Tc <150. As described above, the polyester resin obtained by melting and extruding the polyester resin by controlling the resin temperature in the twin screw extruder and the resin temperature at the outlet of the extruder (strand) is heated by DSC (differential scanning calorimetry). The crystallization temperature Tc (° C.) is measured. If unmelted resin remains, Tc is low (about 120 ° C.), but if Tc is higher than 130 ° C., there is almost no unmelted resin, and if Tc is less than 150 ° C., decomposition of the resin is suppressed and sufficient. It becomes possible to obtain weather resistance.

(Film forming process)
The resin extruded from the extruder outlet 14 of the cylinder 10 is passed through the filter 42 and extruded from the die 40 (for example, to a cooling roll) to be formed into a film.
It is preferable that the humidity is adjusted to 5% RH to 60% RH after the melt (molten resin) is extruded from the die 40 until it contacts the cooling roll (air gap), and 15% RH to 50% RH. It is more preferable to adjust to. By adjusting the humidity in the air gap to the above range, it is possible to adjust the amount of COOH and OH on the film surface, and by adjusting to low humidity, the amount of carboxylic acid on the film surface can be reduced. .
The film thickness is preferably 2 mm to 8 mm, more preferably 2.5 mm to 7 mm, and still more preferably 3 mm to 6 mm. By increasing the thickness of the film, the time required for the extruded melt to cool below the glass transition temperature (Tg) can be lengthened. During this time, COOH groups on the film surface are diffused into the polyester, and the amount of surface COOH can be reduced. Tg represents a glass transition temperature and can be measured based on JIS K7121 or ASTM D3418-82. For example. In the present invention, measurement is performed using a differential scanning calorimeter (DSC) manufactured by Shimadzu Corporation.
Specifically, 10 mg of a polymer such as polyester is weighed as a sample, set in an aluminum pan, and heated at a rate of temperature increase of 10 ° C./min from room temperature to a final temperature of 300 ° C., with a DSC apparatus, the amount of heat with respect to temperature. Was measured as the glass transition temperature.

Moreover, the obtained film-like polyester resin can be made into the polyester film which has desired thickness by performing biaxial stretching in a extending process after that.
The amount of terminal COOH in the polyester film produced by the method of the present invention is preferably in the range of 2 eq / t to 20 eq / t, and preferably in the range of 2 eq / t to 15 eq / t. Is more preferable.

Thus, the polyester film produced by the method of the present invention can further contain additives such as a light stabilizer and an antioxidant.

When containing a light stabilizer, UV degradation can be prevented. Examples of the light stabilizer include a compound that absorbs light such as ultraviolet rays and converts it into heat energy, and a material that captures radicals generated by light absorption and decomposition of the resin and suppresses the decomposition chain reaction. The light stabilizer is preferably a compound that absorbs light such as ultraviolet rays and converts it into heat energy. By containing such a light stabilizer, the effect of improving the partial discharge voltage can be kept high for a long period of time even if it is irradiated with ultraviolet rays continuously for a long period of time. Change, strength deterioration, etc. are prevented.

For example, if an ultraviolet absorber is a range in which other properties of the polyester are not impaired, any of organic ultraviolet absorbers, inorganic ultraviolet absorbers, and combinations thereof are preferably used without particular limitation. Can do. On the other hand, it is desired that the ultraviolet absorber has excellent heat and moisture resistance and can be uniformly dispersed in the resin.

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

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

Furthermore, the polyester film of the present invention contains, in addition to the light stabilizer, for example, a lubricant (fine particles), a colorant, a nucleating agent (crystallization agent), a flame retardant, and the like as necessary. be able to.

<Application>
The polyester film produced by the method of the present invention is a polyester film for solar cell members, specifically, a back surface protective sheet (so-called back sheet) disposed on the back surface opposite to the sunlight incident side of the solar cell power generation module. ), Suitable for applications such as a barrier film substrate.

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

Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples as long as the gist thereof is not exceeded.

Example 1
-Twin screw extruder-
As shown in FIG. 1, the extruder is provided with a screw having the following configuration in a cylinder provided with vents at two locations as shown in FIG. 1, and the temperature can be controlled by dividing the cylinder into nine zones in the longitudinal direction. A double vent type co-rotating mesh type twin screw extruder equipped with a heater (temperature control means) was prepared.
Screw diameter D: 65mm
Length L [mm] / screw diameter D [mm]: 31.5 (width of one zone: 3.5D)
Screw shape: plasticization kneading section just before the first vent, degassing promotion kneading section just before the second vent

After the extruder exit of the twin screw extruder, as shown in FIG. 2, a gear pump, a metal fiber filter and a die having the following constitution are connected, the set temperature of the heater for heating the die is 280 ° C., and the average residence time is 10 minutes.
Gear pump: 2-gear type Filter: Sintered metal fiber filter (pore diameter 20μm)
Die: Lip spacing 4mm

-material-
As a raw material resin, pellets of polyethylene terephthalate (melting point Tm: 257 ° C., intrinsic viscosity IV: 0.78, terminal COOH amount: 15 eq / t, Cp: 2300 J / kgK, crystallized at 160 ° C. with a Henschel mixer) are used. It was. PET pellets having an average major axis: 4.5 mm, an average minor axis: 1.8 mm, and an average length: 4.0 mm were used.

-Melt extrusion-
Each zone (C1 to C9) was melt-extruded with the temperature set as shown in Table 1 below.
The rotation speed of the screw was set to 110 rpm, the raw material resin was supplied from the supply port 12 and heated and melted, and the extrusion rate was set to 250 kg / h to perform melt extrusion.

The melt (melt) extruded from the extruder outlet was passed through a gear pump and a metal fiber filter (pore diameter 20 μm), and then extruded from a die to a cooling (chill) roll. The extruded melt was brought into close contact with the cooling roll using an electrostatic application method. As the cooling roll, a hollow chill roll is used, and the temperature of the cooling roll can be controlled through water as a heating medium.
The conveyance area (air gap) from the die exit to the cooling roll surrounds this conveyance area, and humidity is adjusted to 30% RH by introducing humidity-conditioned air therein. The film thickness was set to 3000 μm by adjusting the extrusion amount of the extruder and the slit width of the die.
As described above, a PET film was obtained.

-Measurement of terminal COOH amount-
About a raw material pellet and the obtained PET film, after dissolving 0.1 g sample in 10 ml of benzyl alcohol, chloroform was further added, the mixed solution was obtained, and the phenol red indicator was dripped at this. This solution was titrated with a reference solution (0.01N KOH-benzyl alcohol mixed solution), and the amount of terminal carboxyl groups was determined from the amount of the reference solution added just before the color of the phenol red indicator changed from yellow to red. AV difference ΔAV obtained for each of the raw material resin and the film was obtained. The results are shown in Table 2 below.

-Measurement of elongation at break-
The PET film cooled by the cooling roll is biaxially stretched (3.4 × 3.8 times), and the breaking elongation of the biaxially stretched film under wet heat conditions (120 ° C. × 100% RH) is halved. Judge by the time to do. It is determined that good weather resistance (hydrolysis resistance) is exhibited in 85 hours or more. The results are shown in Table 2 below.

-Residual evaluation of unmelted foreign matter-
The haze of the film before stretching (thickness 3000 μm) was used as an index. If it is 2.0% or less, it can be evaluated that the stretchability is good. In addition, the measurement of haze was measured based on JISK7136. The results are shown in Table 2 below.

(Examples 2 to 10)
A film was produced in the same manner as in Example 1 except that the conditions such as barrel temperature, cooling method, raw material IV, and chip ratio were changed as shown in Table 1 with respect to Example 1, and the same as in Example 1. Was evaluated. The results are shown in Table 2 below.

(Comparative Examples 1 to 5)
A film was produced in the same manner as in Example 1 except that the conditions such as the barrel temperature, the chip ratio, and the raw material IV were changed as shown in Table 1 with respect to Example 1. The film was evaluated in the same manner as in Example 1. went. The results are shown in Table 2 below.

As shown in Table 2, in the examples, the amount of terminal COOH was 20 eq / t or less, the increase in terminal COOH due to heat melting was suppressed, and a polyester film excellent in hydrolysis resistance could be obtained. . Moreover, in the Example, the haze of the film before extending | stretching is 2.0% or less, and the residual of the unmelted foreign material was suppressed.
On the other hand, in Comparative Examples 1, 3, and 4, the amount of terminal COOH exceeds 20 eq / t, and hydrolysis resistance is lowered due to a large increase in terminal COOH due to heat melting, resulting in insufficient durability. It was.
In Comparative Examples 2, 4, and 5, breakage occurred during film stretching, and film formation suitable for the product was impossible.

The above description of specific embodiments of the present invention is provided for purposes of description and explanation. It is not intended to limit the invention to the precise form disclosed, nor is it intended to be exhaustive. Obviously, many modifications and variations will be apparent to practitioners skilled in this art. The embodiments have been selected to best illustrate the concepts of the invention and their practical application, and thus various embodiments and methods to adapt them to specific applications contemplated by others skilled in the art. It is intended to allow others skilled in the art to understand the present invention so that various modifications can be made.

Japanese Patent Application No. 2011-037187 filed on February 23, 2011 and Japanese Patent Application No. 2011-259663 filed on November 29, 2011 are incorporated herein by reference in their entirety. is there.
All publications, patent applications, and technical standards mentioned in this specification are intended to be specifically and individually incorporated by reference as individual references, patent applications, and technical standards. Is incorporated herein to the same extent as the cited references. It is intended that the scope of the invention be determined by the following claims and their equivalents.

Claims

Polyester resin is supplied to a twin screw extruder, and the resin temperature in the extruder has a maximum value in the range of 295 ° C. to 320 ° C. at a position of 40% to 80% of the total length of the extruder from the upstream end of the extruder. And a step of melt extrusion by controlling the resin temperature at the outlet of the extruder to a range of 275 ° C. to 285 ° C .;
Forming the melt-extruded polyester resin into a film;
The manufacturing method of the polyester film which has this.
The method for producing a polyester film according to claim 1, wherein the temperature of at least a part of the cylinder on the downstream side of the position where the resin temperature in the extruder reaches the maximum value is lower than the melting point of the polyester resin.
The method for producing a polyester film according to claim 2, wherein the temperature of at least a part of the cylinder on the downstream side of the position where the resin temperature in the extruder reaches the maximum value is controlled by a liquid heating medium.
The method for producing a polyester film according to claim 1, further comprising a step of allowing the melt-extruded polyester resin to pass through a filter through a gear pump.
The method for producing a polyester film according to claim 1, further comprising a step of passing the melt-extruded polyester resin through a die before the step of forming the film.
The method for producing a polyester film according to any one of claims 1 to 5, wherein pellets and fluff are supplied as the polyester resin to the extruder with a mass ratio of the fluff being 60% or less.
The method for producing a polyester film according to any one of claims 1 to 5, wherein an intrinsic viscosity of the raw material of the polyester resin is in a range of 0.6 to 0.8.
The method for producing a polyester film according to any one of claims 1 to 5, wherein a melting point Tm of the polyester resin raw material determined by differential scanning calorimetry is in a range of 250 ° C to 260 ° C.
A polyester film in which the amount of terminal COOH of the polyester in the polyester film produced by the method for producing a polyester film according to any one of claims 1 to 5 is in the range of 2 eq / t to 20 eq / t.
A polyester film for a solar cell produced by the production method according to any one of claims 1 to 5.